High-susceptibility of photosynthesis to photoinhibition in the tropical plant Ficus microcarpa L. f. cv. Golden Leaves

BACKGROUND: The tropical plant Ficus microcarpa L. f. cv. Golden Leaves (GL) is a high-light sensitive tropical fig tree in which sun-leaves are yellow and shade-leaves are green. We compared the response of photosynthetic activities to strong light between GL and its wild-type (WT, Ficus microcarpa L. f.). RESULTS: Field measurements of maximum photosystem II (PSII) efficiency (F(v)/F(m)) of intact sun-leaves in GL showed that photo synthetic activity was severely photoinhibited during the daytime (F(v)/F(m) = 0.46) and subsequently recovered in the evening (F(v)/F(m) = 0.76). In contrast, WT did not show any substantial changes of F(v)/F(m) values throughout the day (between 0.82 and 0.78). Light dependency of the CO(2) assimilation rate in detached shade-leaves of GL showed a response similar to that in WT, suggesting no substantial difference in photosynthetic performance between them. Several indicators of photoinhibition, including declines in PSII reaction center protein (D1) content, F(v)/F(m) value, and O(2) evolution and CO(2) assimilation rates, all indicated that GL is much more susceptible to photoinhibition than WT. Kinetics of PAM chlorophyll a fluorescence revealed that nonphotochemical quenching (NPQ) capacity of GL was lower than that of WT. CONCLUSION: We conclude that the photosynthetic apparatus of GL is more highly susceptible to photoinhibition than that of WT

Crassulacean Acid Metabolism Photosynthesis in Pineapple (Ananas comosus (L.) Merr.) Grown under Hydroponic Culture

In order to shorten the cultivation period of pineapple, a crassulacean acid metabolism (CAM) plant, it is important to increase the rate of CO2 exchange rate and improve dry matter production, especially at the early growth stage. When plants are grown under hydroponic conditions, absorption of nutrients and plant water availability are generally increased, and in the case of CAM plants, hydroponics could be expected to improve growth rate through promoting stomatal open during daytime. The objective of this study was to examine the effect of culture method (hydroponic and soil culture) on diurnal changes in gas exchange rate and CO2 balance in pineapple. The daily CO2 balance under hydroponics tended to be higher than under soil culture, especially in Phase-4. This was due to a shortened Phase-3 and a prolonged Phase-4 under hydroponics compared to soil culture. In Phase-4, the CO2 exchange rate was significantly correlated with stomatal conductance, indicating CO2 balance was affected by stomatal activity. Rubisco consumption activated under hydroponic culture may have shortened the duration of Phase-3 when stomatal opening was suppressed. The CO2 balance tended to be increased because of the shortening of Phase-3, resulting in higher dry matter productivity. From these results, it is suggested that hydroponic culture could promote growth in pineapple. However, net assimilation rate under soil culture was equivalent to that under hydroponics. Further study is needed to reveal the relationship between hydroponic cultivation and whole-plant photosynthetic ability

Nursery Growth of Banana (Musa spp.) Plantlets Rooted on Auxin-free and Auxin-supplemented Media

This paper describes the effects of auxin added to the culture medium on main and branch root formation of banana (Musa spp.) shoots and growth characters of the plantlet rooted on the medium with and without auxin. Banana shoots cultured in vitro on Murashige and Skoog medium supplemented with 2 μM 1-naphthylacetic acid (NAA), rooted earlier and also had more adventitious roots than those cultured on the medium without NAA. However, the adventitious roots formed on the medium without NAA showed more lateral branching. Plant height and number of leaves per plantlet in in vitro culture were not influenced by the addition of NAA but under nursery conditions, plantlets rooted without NAA showed better growth in terms of days to the appearance of new leaf, plant height and number of leaves per plant. This might be due to the presence of abundant lateral roots. Even though auxins are generally known to promote rooting, NAA inhibited the formation of lateral roots in Banana plants

Nitrogen use efficiency and drought tolerant ability of various sugarcane varieties under drought stress at early growth stage

The experiment was conducted under glasshouse conditions to evaluate nitrogen use efficiency and drought tolerant ability of the five different sugarcane varieties (including NiF3, Ni9, Ni17, Ni21 and Ni22) under early growth stage from 60 to 120 days after transplanting. The results showed drought stress reduced the photosynthetic rate, growth parameters including plant height, leaf area; partial and total dry weights; and nitrogen use efficiency (NUE) traits including photosynthetic NUE, nitrogen utilization efficiency and biomass NUE of measured sugarcane varieties. The significant differences were found among varieties in growth parameters, dry weights, NUE traits and drought tolerant index (DTI). The significant positive correlations among NUE traits and DTI suggested higher NUEs could support better a tolerant ability to drought stress at the early growth stage. Because of larger contributions, DTIs for aboveground and stalk dry weight could be used as the important DTIs to evaluate drought tolerant ability in sugarcane varieties. Abbreviations Amax: potential photosynthetic rate; DAT: days after transplanting; DTI: drought tolerant index; NL: specific leaf nitrogen content; NUE: nitrogen use efficiency; NUEb: biomass nitrogen use efficiency; NUEt: nitrogen utilization efficiency; PNUE: photosynthetic nitrogen use efficiency; TN: total nitrogen content; TNU: total nitrogen uptake; WW: well-watered; DS: water stress

Water Status of Flower Buds and Leaves as Affected by High Temperature in Heat-Tolerant and Heat-Sensitive Cultivars of Snap Bean (Phaseolus vulgaris L.)

In snap bean {Phaseolus vulgaris L.), flower and pod abscission causes yield reduction under high-temperature conditions. A high temperature enhances transpiration and thus may induce temporal water deficiency in plants in the daytime. The objective of this study was to clarify the effect of a high temperature on the water status of floral organs at their most heat-sensitive stage. We compared the water potential and its components as well as gas exchange between the heat-tolerant cultivar, Haibushi, and heat-sensitive cultivar, Kentucky Wonder, grown under optimal (control) and high-temperature conditions. Haibushi showed higher pollen fertility under high temperature than Kentucky Wonder. Transpiration was enhanced under a high temperature, causing decrease of water potential in leaves and flower buds. The deterioration of water status in floral organs was larger in Kentucky Wonder than in Haibushi. We conclude that temporal deterioration of the water status in flower buds is one of the factors causing pollen damage

Changes in Agronomic and Physiological Traits of Sugarcane Grown with Saline Irrigation Water

In Japan, the highest salt concentration in irrigation water for sugarcane cultivation has been reported to be above 2500 mg L−1, which may cause harmful effects to the crops; however, little information is available on the relationship between the salinity of irrigation water and sugarcane. To investigate its effects on agronomic and physiological traits, a Japanese cultivar, Saccharum spp cv. NiF8, was grown with 0, 200, 500, 1000, 2000, and 3000 mg NaCl L−1 under pot conditions. The treatments significantly lowered leaf area; however, NaCl levels up to 500 mg L−1 did not greatly reduce culm weight and juice sugar concentration. These traits were impaired when the tested cultivar was grown with 1000 mg NaCl L−1 or higher, indicating that salt concentration is desired to be lower than 1000 mg L−1. CO2 assimilation rate was inhibited mainly due to stomatal closure caused by salt stress. The treatments significantly altered Na+, Cl−, and K+ concentrations in juice but not those in leaf, suggesting that juice analysis is an effective method to estimate its salinization status. Culm weight and juice sugar concentration were severely affected as juice conductivity exceeded 900 mS m−1; thereby, sugarcane plants of NiF8 possessing conductivity above this level could be considered salt-stressed where water salinity is a concern

Field Performance of In wiro-propagated and Sucker-derived Plants of Banana (Musa spp.)

The field performance of in vitro-propagated banana (Musa spp.) plants was compared with that of the sucker-derived plants. In vitro-propagated plants established and grew faster, taller and bigger than the conventional sucker-derived plants. The former produced more leaves resulting in a larger total leaf area (8001.5 cm2 per plant) than the latter (6613.1 cm2 per plant) and could be harvested earlier. The former also produced heavier bunches and fruit (15.2 kg for bunch and 200 g per finger of fruit) than the latter (9.0 kg for bunch and 136.4 g per finger of fruit). In this experiment, the in vitro-propagated plants had many intact roots and a bulk of vermiculite around their roots but the sucker-derived plants had many damaged roots at the time of planting. In addition, in vitro-propagated plants started growth earlier and grew faster enabling them to intercept more light for photosynthesis than the sucker-derived plants. This may explain the higher yield in the in vitro-propagated plants. We conclude that in vitro-propagated Shima banana performs better in terms of growth and yield than the sucker-derived plants under field conditions