Abstract
The effects of calcium chloride solution (10 mmol L–1) on mesophyll cell ultrastructure, gas exchange, chlorophyll and carotenoid content, and PSII in tobacco leaf were studied by simulating water deficit conditions via treatment with 25% PEG-6000 for 24 h. The results showed that under drought stress, the mesophyll cell structure and morphology were destroyed, photosynthesis and gas-exchange processes changed, photosynthetic pigment content decreased, and the electron transfer efficiency in PSII reduced. However, compared with the control treatment, under drought conditions, the addition of exogenous calcium could stabilize the structure and function of the chloroplasts, mitochondria, and endomembrane system in the mesophyll cells, maintain normal leaf net photosynthetic rate and gas exchange, alleviate the degree of photosynthetic pigment degradation, and increase the electron transfer energy in the leaves in PSII. As a means of ensuring normal photosynthesis under drought stress, we discovered that the application of exogenous calcium was more important for stabilization of the structure of the organelles, regulation of the osmotic balance, and increase of the photosynthetic pigment content, and proved to be less important for regulation of stomatal opening and closing.
Highlights
Flue-cured tobacco (Nicotiana tabacum Linn.) is one of the most highly valued crops worldwide
The decrease in photosynthetic rate observed during water deficit is not due to an insufficient supply of water, but rather due to limitations of stomatal or nonstomatal factors induced by drought stress (Wise et al 1992)
Seven-week-old tobacco plants were subjected to drought stress by adding 25% polyethylene glycol (PEG)-6000 to the nutrient solution for 24 h
Summary
Flue-cured tobacco (Nicotiana tabacum Linn.) is one of the most highly valued crops worldwide. It is cultivated widely in the southwest of China in mountainous regions that are subjects to severe drought. In flue-cured tobacco production, drought stress affects tobacco growth at the rosette, vigorous growth, flowering, and maturing stages, while the worst impact on the yield and quality occurs at the vigorous growth stage (Wang et al 2009). The value of tobacco depends largely on the yield and quality of its leaves, both of which are affected by photosynthesis. Drought does influence the cell structure and functioning of leaves, and affects light energy capture, light absorption, electron transport, and heat dissipation, and photosynthesis. Increasing the photosynthetic efficiency of leaves under drought stress is significant for flue-cured tobacco production. Calcium can stabilize the cell wall and a variety of organelle membrane structures, promotes NADP synthesis (White and Broadley 2003), is involved in plant hormone transport (Rickauer and Tanner 1986), and
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