| Popis: |
Rooted cuttings of grapevines (Vitis vinifera L. cv. Sultana; syn. Thompson Seedless) were grown under glasshouse conditions and supplied with dilute nutrient solution containing either 0 or 90 mM of added NaCl. Growth and photosynthetic response to salt treatment and subsequent recovery were followed over 80 days. Shoot growth and photosynthesis were reduced by salt treatment. At relatively low concentrations of leaf chloride (< c. 150 mM, on a tissue water basis), photosynthetic reduction was largely due to increased stomatal resistance. Internal disturbances were involved at higher leaf Cl- concentrations (> c. 150 mM) and included an apparent reduction in photochemical efficiency and a faster rate of photorespiration. Levels of fraction I protein, and specific activity of ribulose-1,5-bisphosphate carboxylase measured in vitro, were not reduced by salt treatment. Vines showed remarkable adaptation to salinity insofar as leaves maintained positive turgor despite leaf Cl- concentrations exceeding 300 mM, implying osmotic adjustment. Cessation of salt treatment led to an immediate decrease in leaf Cl-, a promotion of shoot growth and a progressive recovery in photosynthesis accompanied by a marked but not necessarily concurrent reduction in both stomatal and internal resistances. Leaves tolerated Cl- levels up to 200 mM (under glasshouse conditions) without sustaining permanent reduction in photosynthetic activity. New shoots formed subsequent to stress relief are not a prerequisite for Cl- retranslocation from mature leaves as decapitation at the time of stress relief did not prevent attenuation of leaf Cl- or recovery in photosynthesis. |
