Water deficit and associated changes in some photosynthetic parameters in leaves of 'Valencia' orange (Citrus sinensis [L.] Osbeck)

• Published in: Plant physiology (Bethesda) 1988-10, Vol.88 (2), p.375-378
• Main Authors: Vu, J.C.V, Yelenosky, G
• Format: Article
• Language: English
• Subjects: Agriculture; Agronomy. Soil science and plant productions; ASIMILACION; ASSIMILATION; BALANCE HIDRICO; BILAN HYDRIQUE; Biological and medical sciences; CARBON DIOXIDE; CITRUS SINENSIS; Dehydration; DIOXIDO DE CARBONO; DIOXYDE DE CARBONE; Economic plant physiology; Environmental and Stress Physiology; Enzyme activity; Enzymes; FEUILLE; FOTOSINTESIS; Fundamental and applied biological sciences. Psychology; HOJAS; LEAVES; Metabolism; Net assimilation, photosynthesis, carbon metabolism. Photorespiration, respiration, fermentation (anoxia, hypoxia); Nutrition. Photosynthesis. Respiration. Metabolism; PHOTOSYNTHESE; PHOTOSYNTHESIS; Photosynthesis, respiration. Anabolism, catabolism; Physiological assimilation; Plant physiology and development; Plants; Stomatal conductance; Transpiration; WATER BALANCE
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.88.2.375

Photosynthetic CO2 assimilation, transpiration, ribulose-1,5-bisphosphate carboxylase (RuBPCase), and soluble protein were reduced in leaves of water-deficit (stress) 'Valencia' orange (Citrus sinensis [L.] Osbeck). Maximum photosynthetic CO2 assimilation and transpiration, which occurred before midday for both control and stressed plants, was 58 and 40%, respectively, for the stress (-2.0 megapascals leaf water potential) as compared to the control (-0.6 megapascals leaf water potential). As water deficit became more severe in the afternoon, with water potential of -3.1 megapascals for the stressed leaves vs. -1.1 megapascals for control leaves, stressed-leaf transpiration declined and photosynthetic CO2 assimilation rapidly dropped to zero. Water deficit decreased both activation and total activity of RuBPCase. Activation of the enzyme was about 62% (of fully activated enzyme in vitro) for the stress, compared to 80% for the control. Water deficit reduced RuBPCase initial activity by 40% and $\text{HCO}_{3}{}^{-}/\text{Mg}^{2+}$-saturated activity by 22%. However, RuBPCase for both stressed and control leaves were similar in $K_{\text{cat}}$ (25 moles CO2 per mole enzyme per second) and Km for CO2 (18.9 micromolar). Concentrations of RuBPCase and soluble protein of stressed leaves averaged 80 and 85%, respectively, of control leaves. Thus, reductions in activation and concentration of RuBPCase in Valencia orange leaves contributed to reductions in enzyme activities during water-deficit periods. Declines in leaf photosynthesis, soluble protein, and RuBPCase activation and concentration due to water deficit were, however, recoverable at 5 days after rewatering.