Biochemical, Physiological and Morphological Responses of Sugar Beet to Salinization

Abstract

Biochemical, physiological and morphological responses of sugar beet grown on sandy soil under three levels of NaCl salinity in irrigation water, i.e. control, 3000 & 6000 ppm was studied in pot experiment. Results showed that root fresh weight linearly decreased by increasing NaCl salinity levels up to 6000 ppm, but sucrose percentage in root was significantly increased. On the other hand, increasing NaCl levels resulted in significant increase of Na content in both of shoot and root Meanwhile, K content in shoot was sharplydecreased but K content in root didn t significantly differ by increasing NaCl levels. Also, under salinity results indicated a strongly negative correlation between shoot osmotic potential and shoot Na content while it was mainly with sucrose concentration in root. Thus, sugar beet plant has an active mechanism to include higher amount of Na in leaves and utilizes it to regulate leave osmotic potential under saline condition. Despite of this mechanism the transpiration rate and stomatal conductance showed significant decrease byincreasing NaCl levels up to 6000 ppm. Moreover, stomatal behavior and stomatalmorphology revealed a gradual response to the level of NaCl salinity used. Stomatal density, area and pore area strongly decreased by raising NaCl level from control to 3000 ppm with no effect on stomatal closure. No further response was shown for stomatal area by increasing NaCl from 3000 to 6000 ppm, while stomatal closure recorded 60% in lower & 30% in upper leaf surface at 6000 ppm NaCl level. Generally, it could be pointed out that the decrease ofsugar beet root fresh weight at low salinity level (3000 ppm) may be due to osmotical stress while at high level of NaCl (6000 ppm) it was attributed to toxic effect of higher Na accumulation on photosynthesis which led to closed stomata in order to inhibit Na transport into leaves.