Sensitividade do maracujazeiro‑amarelo à radiação ultravioleta‑B

The objective of this work was to evaluate the effects of UV‑B radiation on the vegetative growth and on the gas exchange characteristics of passion fruit plants (Passiflora edulis) grown in greenhouse. The average unweighted UV‑B radiation near the apex of the plants was 8 W m-2 for the UV‑B treatment (high UV‑B), and 0.8 W m-2 for the control plants (low UV‑B). Plants were irradiated with UV‑B for 7 hours per day, centered on solar noon, during 16 days. High UV‑B radiation resulted in lower shoot dry matter accumulation per plant. The content of UV‑B absorbing compounds and anthocyanins was increased in the plants exposed to high UV‑B radiation, when compared with the control. UV‑B radiation did not affect stomatal conductance or transpiration rate, but reduced photosynthesis and instantaneous water‑use efficiency, and increased intercellular CO2 concentration. The accumulation of UV‑B‑absorbing compounds and anthocyanins did not effectively shield plants from supplementary UV‑B radiation, since the growth and photosynthetic processes were significantly reduced.O objetivo deste trabalho foi avaliar o efeito da radiação UV‑B no crescimento vegetativo e nas características das trocas gasosas de plantas de maracujazeiro‑amarelo (Passiflora edulis), cultivadas em casa de vegetação. A radiação média não ponderada de UV‑B próximo ao topo das plantas foi de 8 W m-2, para plantas tratadas com UV‑B (alta UV‑B), e de 0,8 W m-2 para plantas controle (baixa UV‑B). As plantas foram irradiadas com UV‑B por 7 horas por dia, centralizadas ao redor do meio‑dia, durante 16 dias. Alta radiação de UV‑B reduziu o acúmulo de matéria seca da parte aérea da planta. O conteúdo de compostos que absorvem UV‑B e de antocianinas foi aumentado nas plantas expostas à alta radiação UV‑B, quando comparado às plantas controle. A radiação UV‑B não alterou a condutância estomática ou a taxa de transpiração, mas reduziu a fotossíntese e a eficiência instantânea do uso da água, e aumentou a concentração intercelular de CO2. O acúmulo de compostos que absorvem UV‑B e antocianinas não protegeram de forma efetiva as plantas contra o aumento da radiação suplementar UV‑B, visto que o crescimento e os processos fotossintéticos foram significativamente reduzidos

Effect of nitrogen supply on growth and photosynthesis of sunflower plants grown in the greenhouse

The effects of nitrogen availability on growth and photosynthesis were followed in plants of sunflower (Helianthus annuus L., var. CATISSOL-01) grown in the greenhouse under natural photoperiod. The sunflower plants were grown in vermiculite under two contrasting nitrogen supply, with nitrogen supplied as ammonium nitrate. Higher nitrogen concentration resulted in higher shoot dry matter production per plant and the effect was apparent from 29 days after sowing (DAS). The difference in dry matter production was mainly attributed to the effect of nitrogen on leaf production and on individual leaf dry matter. The specific leaf weight (SLW) was not affected by the nitrogen supply. The photosynthetic CO2 assimilation (A) of the target leaves was remarkably improved by high nitrogen nutrition. However, irrespective of nitrogen supply, the decline in photosynthetic CO2 assimilation occurred before the end of leaf growth. Although nitrogen did not change significantly stomatal conductance (gs), high-N grown plants had lower intercellular CO2 concentration (C-i) when compared with low-N grown plants. Transpiration rate (E) was increased in high-N grown plants only at the beginning of leaf growth. However, this not resulted in lower intrinsic water use efficiency (WUE). (C) 2004 Elsevier B.V.. All rights reserved

Growth and physiological responses of sunflower plants exposed to ultraviolet-B radiation

Os efeitos da radiação UV-B foram estudados em plantas de girassol (Helianthus annuus L. cv. Catissol-01) cultivadas em casa de vegetação sob condições fotoperiódicas naturais. As plantas receberam aproximadamente 0,60W m-2 (controle) ou 4,0W m-2 (+UV-B) de radiação UV-B por 7h d-1, centralizadas ao redor do meio-dia. A irradiação com UV-B foi iniciada 15 dias após a semeadura. Plantas sob alta radiação UV-B durante 12 ou 21 dias não apresentaram diferenças em matéria seca da parte aérea, peso foliar específico ou compostos que absorvem UV-B, quando comparadas com o controle. Alta radiação UV-B reduziu a taxa de fotossíntese (A) somente na primeira coleta, sendo acompanhada por uma redução na condutância estomática (g s) e na taxa de transpiração. A inibição da fotossíntese não pode ser somente explicada pela redução na g s, visto que a concentração intercelular de CO2 não foi alterada pelo aumento na radiação UV-B. O conteúdo total de clorofila não foi afetado pelo aumento na radiação UV-B nas duas coletas. No entanto, o conteúdo de clorofila a e a razão clorofila a/b foram reduzidas na primeira coleta. Sob alta radiação UV-B, houve aumento na fluorescência mínima na primeira coleta. Porém, a razão entre a fluorescência variável e a fluorescência máxima das folhas adaptadas ao escuro não foi alterada. Estes resultados sugerem que o atual nível de radiação solar UV-B afeta o desempenho das plantas de girassol, embora a massa seca da parte aérea não seja afetada.The effects of UV-B radiation were studied in sunflower plants (Helianthus annuus L. cv. Catissol-01) growning in greenhouse under natural photoperiod conditions. The plants received approximately 0.60Wm-2 (control) or 4.0Wm-2 (+UV-B) of UV-B radiation for 7h d-1, centered around solar noon from 15 days after sowing. Compared to the control, plants exposed to high UV-B radiation for 12 or 21 days did not show any difference in shoot dry matter, specific leaf weight or UV-B absorbing compounds. Enhanced UV-B radiation caused a significant inhibition of photosynthesis (A) only in the first sampling and this was accompained by reduction in stomatal conductance (g s) and transpiration rate. The inhibition in A can not be fully explained by reduction in g s since intercellular CO2 concentration was not affected by UV-B radiation. In both samplings, the total chlorophyll content was not affected by enhanced UV-B radiation whereas in the first sampling, the chlorophyll a and the ratio of chlorophyll a/b were reduced. Enhanced UV-B radiation increased the minimal fluorescence yield, but did not alter the ratio of variable to maximal fluorescence yield of dark adapted leaves. Overall, this study suggests that the present level of solar UV-B radiation affects sunflower plants performance even though the shoot dry biomass may not be affected.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Sensitivity of yellow passion fruit plants to ultraviolet-B radiation

The objective of this work was to evaluate the effects of UV-B radiation on the vegetative growth and on the gas exchange characteristics of passion fruit plants (Passiflora edulis) grown in greenhouse. The average unweighted UV-B radiation near the apex of the plants was 8 W m-2 for the UV-B treatment (high UV-B), and 0.8 W m-2 for the control plants (low UV-B). Plants were irradiated with UV-B for 7 hours per day, centered on solar noon, during 16 days. High UV-B radiation resulted in lower shoot dry matter accumulation per plant. The content of UV-B absorbing compounds and anthocyanins was increased in the plants exposed to high UV-B radiation, when compared with the control. UV-B radiation did not affect stomatal conductance or transpiration rate, but reduced photosynthesis and instantaneous water‑use efficiency, and increased intercellular CO2 concentration. The accumulation of UV-B-absorbing compounds and anthocyanins did not effectively shield plants from supplementary UV-B radiation, since the growth and photosynthetic processes were significantly reduced.O objetivo deste trabalho foi avaliar o efeito da radiação UV-B no crescimento vegetativo e nas características das trocas gasosas de plantas de maracujazeiro-amarelo (Passiflora edulis), cultivadas em casa de vegetação. Aradiação média não ponderada de UV-B próximo ao topo das plantas foi de 8 W m-2 , para plantas tratadas com UV-B (alta UV-B), e de 0,8 W m-2 para plantas controle (baixa UV-B). As plantas foram irradiadas com UV-B por 7 horas por dia, centralizadas ao redor do meio-dia, durante 16 dias. Alta radiação de UV-B reduziu o acúmulo de matéria seca da parte aérea da planta. O conteúdo de compostos que absorvem UV-B e de antocianinas foi aumentado nas plantas expostas à alta radiação UV-B, quando comparado às plantas controle. A radiação UV-B não alterou a condutância estomática ou a taxa de transpiração, mas reduziu a fotossíntese e a eficiência instantânea do uso da água, e aumentou a concentração intercelular de CO2. O acúmulo de compostos que absorvem UV-B e antocianinas não protegeram de forma efetiva as plantas contra o aumento da radiação suplementar UV‑B, visto que o crescimento e os processos fotossintéticos foram significativamente reduzidos

The Influence of Municipal Treated Wastewater on Morpho-Physiological Characteristics of Eucalyptus Plants

The effects of municipal-treated wastewater on growth and gas exchange characteristics were studied in eucalyptus plants cultivated in a greenhouse under continuous sub irrigation with 70 % Long Ashton solution as a control, 100 % treated wastewater, and treated wastewater diluted 50 % with tap water. Irrigation with wastewater resulted in a reduction of total dry matter per plant and the shoot-to-root ratio and increased specific leaf mass, irrespective of the dilution. The gas exchange characteristics were adversely affected by the irrigation with wastewater, with photosynthetic rates been negatively affected. Total chlorophyll and carotenoids content were reduced in plants grown under treated wastewater. The results demonstrated that when the eucalyptus plants were grown under treated wastewater as the only source of mineral nutrients they were able to produce nearly 50 % of the dry matter produced by the plants grown under appropriate mineral nutrient supply, irrespective of the dilution. Therefore, the contribution of mineral nutrients and organic matter from the treated wastewater used as agricultural irrigation will be significant in lower the fertilizer rates without reducing dry matter production per plant

Nitric oxide reduces oxidative damage induced by water stress in sunflower plants

Drought is one of the main environmental constraints that can reduce plant yield. Nitric oxide (NO) is a signal molecule involved in plant responses to several environmental stresses. The objective of this study was to investigate the cytoprotective effect of a single foliar application of 0, 1, 10 or 100 µM of the NO donor sodium nitroprusside (SNP) in sunflower plants under water stress. Water stressed plants treated with 1μM SNP showed an increase in the relative water content compared with 0 μM SNP. Drought reduced the shoot dry weight but SNP applications did not result in alleviation of drought effects. Neither drought nor water stress plus SNP applications altered the content of photosynthetic pigments. Stomatal conductance was reduced by drought and this reduction was accompanied by a significant reduction in intercellular CO2 concentration and photosynthesis. Treatment with SNP did not reverse the effect of drought on the gas exchange characteristics. Drought increased the level of malondialdehyde (MDA) and proline and reduced pirogalol peroxidase (PG-POD) activity, but did not affect the activity of superoxide dismutase (SOD). When the water stressed plants were treated with 10 μM SNP, the activity of PG-POD and the content of proline were increased and the level of MDA was decreased. The results show that the adverse effects of water stress on sunflower plants are dependent on the external NO concentration. The action of NO may be explained by its ability to increase the levels of antioxidant compounds and the activity of ROS-scavenging enzymes

Ultraviolet-B and water stress effects on growth, gas exchange and oxidative stress in sunflower plants

The effects and interaction of drought and UV-B radiation were studied in sunflower plants (Helianthus annuus L. var. Catissol-01), growing in a greenhouse under natural photoperiod conditions. The plants received approximately 1.7 W m(-2) (controls) or 8.6 W m(-2) (+UV-B) of UV-B radiation for 7 h per day. The UV-B and water stress treatments started 18 days after sowing. After a period of 12 days of stress, half of the water-stressed plants (including both UV-B irradiated or non-irradiated) were rehydrated. Both drought and UV-B radiation treatments resulted in lower shoot dry matter per plant, but there was no significant interaction between the two treatments. Water stress and UV-B radiation reduced photosynthesis, stomatal conductance and transpiration. However, the amplitude of the effects of both stressors was dependent on the interactions. This resulted in alleviation of the negative effect of drought on photosynthesis and transpiration by UV-B radiation as the water stress intensified. Intercelluar CO(2) concentration was initially reduced in all treatments compared to control plants but it increased with time. Photosynthetic pigments were not affected by UV-B radiation. Water stress reduced photosynthetic pigments only under high UV-B radiation. The decrease was more accentuated for chlorophyll a than for chlorophyll b. As a measure for the maximum efficiency of photosystem II in darkness F (v)/F (m) was used, which was not affected by drought stress but initially reduced by UV-B radiation. Independent of water supply, UV-B radiation increased the activity of pirogalol peroxidase and did not increase the level of malondialdehyde. on the other hand, water stress did not alter the activity of pirogalol peroxidase and caused membrane damage as assessed by lipid peroxidation. The application of UV-B radiation together with drought seemed to have a protective effect by lowering the intensity of lipid peroxidation caused by water stress. The content of proline was not affected by UV-B radiation but was increased by water stress under both low and high UV-B radiation. After 24 h of rehydration, most of the parameters analyzed recovered to the same level as the unstressed plants

Diferentes respostas entre folhas adultas e jovens de plantas de girassol ao estresse oxidativo causado pelo déficit hídrico

Os efeitos do estresse hídrico e da reidratação nas trocas gasosas juntamente com alterações na lipoperoxidação e atividade da pirogalol peroxidase (PG-POD) foram estudados em folhas adultas e jovens de plantas de girassol (Helianthus annuus L.) cultivadas em casa de vegetação. O estresse hídrico reduziu a fotossíntese (P N), a condutância estomática (g s) e a transpiração (E) nas folhas adultas e jovens. No entanto, a amplitude da redução foi dependente da idade da folha. A concentração intercelular de CO2 (Ci) aumentou nas folhas adultas, mas não apresentou alteração nas folhas jovens sob condições de estresse hídrico. A eficiência instantânea do uso da água (WUE) nas folhas adultas e estressadas foi reduzida em comparação com o controle, enquanto que, nas folhas jovens e estressadas, não foi alterada. Após 24h de reidratação, as folhas apresentaram valores semelhantes aos dos controles em todos os parâmetros relacionados com as trocas gasosas, exceto gs e E nas folhas adultas. O estresse hídrico não ativou a PG-POD, independente da idade da folha, e após a reidratação a atividade da PG-POD foi aumentada apenas nas folhas adultas. O estresse hídrico aumentou o teor de malondialdeído (MDA) nas folhas adultas e jovens. Os resultados sugerem que as folhas jovens são mais susceptívies ao déficit hídrico em termos de trocas gasosas que as folhas adultas, embora ambas tenham sido expostas ao estresse oxidativo.The effects of water stress and rehydration on leaf gas exchange characteristics along with changes in lipid peroxidation and pirogalol peroxidase (PG-POD) were studied in mature and in young leaves of sunflower (Helianthus annuus L.), which were grown in a greenhouse. Water stress reduced photosynthesis (Pn), stomatal conductance (g s), and transpiration (E) in both young and mature leaves. However, the amplitude of the reduction was dependent on leaf age. The intercellular CO2 concentration (Ci) was increased in mature leaves but it was not altered in young leaves. Instantaneous water use efficiency (WUE) in mature stressed leaves was reduced when compared to control leaves while in young stressed leaves it was maintained to the same level as the control. After 24h of rehydration, most of the parameters related to gas exchange recovered to the same level as the unstressed plants except gs and E in mature leaves. Water stress did not activated PG-POD independently of leaf age. However, after rehydration the enzyme activity was increased in mature leaves and remained to the same as the control in young leaves. Malondialdehyde (MDA) content was increased by water stress in both mature and young leaves. The results suggest that young leaves are more susceptible to water stress in terms of gas exchange characteristics than mature leaves although both went through oxidative estresse