Conocarpus Lancifolius under Semi-Arid Conditions in the State of Kuwait: Ecophysiological, Biochemical and Cytological Studies

missing

Studies were conducted on the morphological, eco-physiological and biochemical adaptations of Conocarpus lancifolius that probably enabled the species to withstand semi-arid conditions. Plants were grown in variable experimental stress conditions and their response to increase in temperature, chilling, drought and salinity stresses with respect to growth rate, photosynthesis, leaf fluorescence, accumulation of the biochemical defense compounds such as ascorbic acid and phenolics, reducing sugars, and the ability of the species to synthesize dehydrins and heat shock proteins (HSPs) were investigated. Leaf succulence and sclerophyll showed that the species exhibited xerophytic characteristics. Shoot growth and leaf size were reduced regardless of the stress factor. Stressed plants developed smaller, grayish green, and sclerophylous leaves. Shoot length and proliferation increased with increase in temperature. Morphological injury due to lower temperatures included leaf tip burn, necrotic spots and death of young leaves. Histological damage included unstacking, and distortion of grana, disintegration of the thylakoid membranes and the tonoplast. Similarly, leaf fluorescence and the photochemical efficiency of PS II (Fv/Fm), electron transport rate (ETR) and photosynthetic rate (Ps) declined at 5 and 10°C or after chilling but increased when plants were re-watered. Plants drought-chilled for 6-9 h recovered when re-watered after 3 days. Drought stress did not appear to confer chilling tolerance to C. lancifolius. Heat shock protein(70 kDa) was produced in increasing amounts after 3-4 h at temperatures above 30o C and at 50o C an additional 90 kDa protein was produced. Total plant phenols increased significantly from 5.37 mg/g DW ±0.059 (SEM) in controls to 8.75 mg/g DW ±0.037 (SEM) in water deprived seedlings. A consistent increase in phenols was also observed with increasing temperature and under prolonged salt stress conditions. However, concentration of phenols decreased with increasing concentration of polyethylene glycol (PEG). Data from the current study provides sufficient evidence to show that tolerance of C. lancifolius to extreme temperature stress is linked with the synthesis of ascorbic acid indicating its biochemical role in protecting plant cells from reactive oxygen species induced by stress. Temperature stress significantly increased ascorbic acid concentrations from 5.33 µg/g FW at 10o C to 7.38 µg/g FW at 40o C treated plants at which growth was at its maximal. A consistent decrease in the concentration of ascorbic acid, however, was observed in water-deprived, PEG and salt-stressed seedlings. Cellular localization of ascorbic acid in plants exposed to high temperature was studied using light microscopy techniques. Initial results indicate deposition of ascorbic acid in leaf mesophyll cell walls. Cytological investigation implementing various methods revealed that the chromosome number for both morphotypes was the same. The various cytological and genetic analyses carried out during this investigation all confirmed that genetically both morphotypes were the same, and the differences in size and color of the leaves may be due to environmental factors.