Regulación de la abscisión de los frutos cítricos inducida por el estrés hídrico y la rehidratación

Los cítricos presentan un comportamiento característico en cuanto a la abscisión de hojas inducida por la carencia de agua. Cuando los árboles se someten a estrés hídrico, las hojas pierden turgencia pero permanecen unidas al árbol hasta que el estrés hídrico se libera mediante irrrigación o lluvia, momento en que se produce una abscisión súbita (Gómez-Cadenas et al., 1996). Por otro lado, se ha demostrado que el ABA y el ACC, se acumulan en las raíces en condiciones de estrés hídrico y se reducen a niveles basales inmediatamente después de la rehidratación. El estrés hídrico sin embargo, induce la acumulación de ABA en las hojas sin incrementar los niveles de ACC y etileno en estas condiciones. La rehidratación de las plantas reduce la concentración de ABA e incrementa los niveles de ACC y etileno en las hojas, produciendo, además, la abscisión foliar. Por lo tanto se sugiere que los niveles de ABA, la primera señal hormonal sensible al estrés hídrico, modulan la síntesis de ACC radicular y, por consiguiente, el incremento posterior de etileno que dispara el proceso de abscisión foliar (Gómez-Cadenas et al., 1996). Lo anteriormente expuesto nos sugiere que probablemente la abscisión de frutos inducida por la deficiencia hídrica y rehidratación también está regulada por los niveles de ABA. Esta es una hipótesis que pretendemos comprobar en este trabajo

Use of Persistent Analogs of Abscisic Acid as Palliatives against Salt-stress Induced Damage in Citrus Plants

The effectiveness of several abscisic acid (ABA) analogs as palliatives against salt stress in intact citrus plants has been tested in this work. The effect of ABA, 8¢-methylene ABA, 8¢-acetylene ABA, ABA methyl ester, 8¢-methylene ABA methyl ester, and 8¢-acetylene ABA methyl ester on citrus responses to salt stress was studied on 2-year-old grafted plants. Leaf abscission, chloride accumulation, ethylene production, and net photosynthetic rate were the parameters used to characterize the performance of plants under stress. Data indicate that 8¢-methylene ABA was the most effective compound in delaying the deleterious effects of high salinity on citrus plants. Its regular application reduced leaf chloride concentration, ethylene production, and leaf abscission. Furthermore, it delayed the depletion of CO2 assimilation under these adverse conditions. Abscisic acid and 8¢-acetylene ABA also reduced salt-stress induced injuries in citrus, although to a lower extent. Neither ABA methyl ester nor its 8¢-C modified analogs showed biological activity in these assays

Effects of salt stress on plant growth, abscisic acid and salicylic acid in own-rooted cultivars of Vitis vinifera L.

Aim of study: In most areas of vineyards worldwide, cultivars are frequently grafted on specific rootstocks to avoid Daktulosphaira vitifoliae pest attack. Nevertheless, the absence of this pest in Canary Islands allowed the chance to conserve and cultivate traditional or new own-rooted genotypes without the requirement of the rootstocks. To investigate the responses of own-rooted genotypes of Vitis vinifera L. to salt stress conditions, ‘Castellana Negra’ (‘CN’) and ‘Negramoll’ (‘Ne’) were used with the aim to characterize their morphological and physiological responses.Area of study: Canary Islands, Spain.Material and methods: The effects of NaCl stress on growth, abscisic acid (ABA), salicylic acid (SA) and proline were assessed in ‘CN’ and ‘Ne’ under greenhouse conditions.Main results: In ‘CN’, the decrease of leaf number in stressed plants was lower and started eleven days later than in ‘Ne’. Salt stress also reduced stomatal conductance (gs), although such decrease took place earlier in ‘CN’ than in ‘Ne’. ABA and SA concentrations in ‘CN’ leaves were 2-fold higher than those of ‘Ne’. Salt stress increased leaf ABA and SA content in both genotypes, compared to control. In conclusion, ABA and SA appear to be involved in grapevines responses to salinity and suggest that exogenous SA could be useful to mitigate the stress impacts.Research highlights: ‘CN’ exhibited a better response than ‘Ne’ through the delay of salt injury establishment, and the dissimilar responses between ‘CN’ and ‘Ne’ seem to be associated to the higher accumulation of ABA and SA under salt stress

Plant Growth and Fruit Nutrient Changes in Carica papaya L. Genotypes Subjected to Regulated Deficit Irrigation

The current genotypes of Carica papaya L. cultivated worldwide are considered relatively tolerant or sensitive to drought conditions, depending specifically on the cultivar features and the severity of water shortage. In this work an experimental field was established by subjecting “Intenzza” and “Siluet” to the following water regimes: Control (“CT”), plants irrigated at field capacity (100%); Moderate Deficit Irrigation (“MDI”, watered at 66%); and Severe Deficit Irrigation (“SDI”, watered at 50%). The results indicated that water deficit decreases leaf number leading to a decline of total leaf area, being “Intenzza” equally affected by “SDI” and “MDI”, whereas in “Siluet” the major decrease was induced by “SDI”. Regarding fruit development, in “Intenzza”, “MDI” and “SDI” did not affect fruit number except two dates (120 and 202 DAT), decreased fruit fresh weight (FW), and increased total soluble solutes (TSS) levels, while in “Siluet” only “SDI” reduced fruit FW and watering systems did not change TSS, suggesting a better performance of this cultivar under “MDI”. In addition, drought did not impair fruit mineral concentrations excepting in few dates, and in such cases stressed fruits accumulated a slight minor or even major concentration of some nutrients than control, maintaining consequently suitable organoleptic quality

Plant Growth and Fruit Nutrient Changes in <i>Carica papaya</i> L. Genotypes Subjected to Regulated Deficit Irrigation

The current genotypes of Carica papaya L. cultivated worldwide are considered relatively tolerant or sensitive to drought conditions, depending specifically on the cultivar features and the severity of water shortage. In this work an experimental field was established by subjecting “Intenzza” and “Siluet” to the following water regimes: Control (“CT”), plants irrigated at field capacity (100%); Moderate Deficit Irrigation (“MDI”, watered at 66%); and Severe Deficit Irrigation (“SDI”, watered at 50%). The results indicated that water deficit decreases leaf number leading to a decline of total leaf area, being “Intenzza” equally affected by “SDI” and “MDI”, whereas in “Siluet” the major decrease was induced by “SDI”. Regarding fruit development, in “Intenzza”, “MDI” and “SDI” did not affect fruit number except two dates (120 and 202 DAT), decreased fruit fresh weight (FW), and increased total soluble solutes (TSS) levels, while in “Siluet” only “SDI” reduced fruit FW and watering systems did not change TSS, suggesting a better performance of this cultivar under “MDI”. In addition, drought did not impair fruit mineral concentrations excepting in few dates, and in such cases stressed fruits accumulated a slight minor or even major concentration of some nutrients than control, maintaining consequently suitable organoleptic quality

Abscisic acid, indole-3-acetic acid and mineral–nutrient changes induced by drought and salinity in longan (Dimocarpus longan Lour.) plants

Longan species (Dimocarpus longan Lour.) exhibit a high agronomic potential in many subtropical regions worldwide; however, little is known about its responses to abiotic stress conditions. Drought and salinity are the most environmental factors inducing negative effects on plant growth and development. In order to elucidate the responses of longan to drought and salinity, seedlings were grown under conditions of drought and salt stresses. Drought was imposed by suspending water supply leading to progressive soil dehydration, and salinity was induced using two concentrations of NaCl, 100 and 150 mM in water solution, for 64 days. Data showed that salt concentrations increased foliar abscisic acid (ABA) and only 150 mM NaCl reduced indole-3-acetic acid (IAA) and increased proline levels. NaCl treatments also increased Na+ and Cl− content in plant organs proportionally to salt concentration. Drought increased leaf ABA but did not change IAA concentrations, and also increased proline synthesis. In addition, drought and salt stresses reduced the photosynthesis performance; however, only drought decreased leaf growth and relative leaf water content. Overall, data indicate that under severe salt stress, high ABA accumulation was accompanied by a reduction of IAA levels; however, drought strongly increased ABA but did not change IAA concentrations. Moreover, drought and high salinity similarly increased (or maintained) ion levels and proline synthesis. Data also suggest that ABA accumulation may mitigate the impact of salt stress through inducing stomatal closure and delaying water loss, but did not mediate the effects of long-term drought conditions probably because leaves reached a strong dehydration and the role of ABA at this stage was not effective to detain leaf injuries

Delay of early fruitlet abscission by branch girdling in citrus coincides with previous increases in carbohydrate and gibberellin concentrations

Current evidence in citrus indicates that gibberellins (GAs) are main determinants of early fruit set while subsequent growth of developing fruits is mostly dependent upon carbohydrate availability. In this work, branch girdling performed at anthesis in Satsuma mandarin (Citrus unshiu (Mak.) Marc.) cv. Okitsu transitorily reduced early abscission rates (12-32 days after anthesis, DAA) delaying initially the process of natural fruitlet drop. The effects of girdling on growth, gibberellin (GA) and carbohydrate concentrations in developing ovaries and fruitlets were assessed during this initial growth stage (0-69 DAA). In girdled branches, abscission rate reduction was preceded by elevated concentrations of carbohydrate and GA in developing ovaries and fruitlets. Girdling at anthesis stimulated higher hexose (21 DAA) and starch (6-20 DAA) concentrations and also higher GA(1) (6 DAA), GA(19) (13-20 DAA) and GA(20) (6-20 DAA). The results established a relationship between the reduction of early abscission rates and higher concentrations of carbohydrates and GAs induced by girdling in developing fruitlets. These findings revealed that girdling certainly increased GA concentration and strongly suggested that its effect on early fruitlet abscission delay is likely mediated by both GA and carbohydrates

Hormonal and Hydroxycinnamic Acids Profiles in Banana Leaves in Response to Various Periods of Water Stress

The pattern of change in the endogenous levels of several plant hormones and hydroxycinnamic acids in addition to growth and photosynthetic performance was investigated in banana plants (Musa acuminata cv. “Grand Nain”) subjected to various cycles of drought. Water stress was imposed by withholding irrigation for six periods with subsequent rehydration. Data showed an increase in abscisic acid (ABA) and indole-3-acetic acid (IAA) levels, a transient increase in salicylic acid (SA) concentration, and no changes in jasmonic acid (JA) after each period of drought. Moreover, the levels of ferulic (FA) and cinnamic acids (CA) were increased, and plant growth and leaf gas exchange parameters were decreased by drought conditions. Overall, data suggest an involvement of hormones and hydroxycinnamic acids in plant avoidance of tissue dehydration. The increase in IAA concentration might alleviate the senescence of survival leaves and maintained cell elongation, and the accumulation of FA and CA could play a key role as a mechanism of photoprotection through leaf folding, contributing to the effect of ABA on inducing stomatal closure. Data also suggest that the role of SA similarly to JA might be limited to a transient and rapid increase at the onset of the first period of stress

Antagonistic changes between abscisic acid and gibberellins in citrus fruits subjected to a series of different water conditions

The relationship between absicisic acid (ABA) and gibberellin (GA) changes in developing fruitlets from both Clementina (Citrus clementina, Hort ex Tan) and Okitsu (Citrus unshiu, (Mak) Marc.) trees subjected to changing water conditions was investigated. The treatments consisted of a series of water stress, rainfall, and re-irrigation periods. To confirm the effectiveness of the imposed water changes, leaf water potential and soil moisture were measured. The data indicated that there were antagonistic changes between ABA and GA(20), because in both species ABA increased and GA(20) decreased during water stress, whereas re-hydration via either rainfall or irrigation reduced ABA but increased GA20. In addition, the data indicated that during water stress GA1 also decreased, whereas GA(8) did not change. After re-hydration, however, levels of GA(20) products, in general were rather dependent upon the hormonal levels induced in the previous water status. In conclusion, the results showed the occurrence of antagonistic changes between the levels of ABA and GA(20) in developing citrus fruitlets subjected to changing water conditions. The data might suggest that gibberellin 20-oxidase is regulated by water stress in citrus fruits