PLANT BIOSYSTEMS, 136 (2) 277-288 2003 Effect of kinetin on photosynthetic activity and carbohydrate content in waterlogged or seawater-treated Vigna sinensis and Zea mays plants O. A. EL-SHAHABY, M. M. NEMAT ALLA, M. E. YOUNIS AND Z. M. EL-BASTAWISY received 14 April 2001; revised version accepted 16 January 2002 ABSTRACT - Waterlogging decreased carotenoids content of Vigna sinensis and Zea mays whilst salinity provoked increases in the first and decreases in the second. Both treatments showed significant reductions in chlorophylls content and in photosynthetic activity (Hill reaction and 14 CO 2 -light fixation). Meanwhile, a significant decrease in the activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) was detected in both plants. These reductions could result in losses in the photosynthetic activity with a drop in the net formation of carbohydrates. Waterlogging markedly increased glucose and sucrose in shoots and roots of both species throughout the experimental period but greatly decreased polysaccharides, whilst salinity reduced all carbohydrate fractions. Foliar application of 50 ppm kinetin to treated plants mostly counterbalanced the observed changes in pigments as well as in Hill reaction and 14 CO 2 assimilation. Also kinetin rendered levels of carbohydrate fractions in shoots and roots of treated plants and activity of Rubisco most likely to reach control values. The increased levels of glucose and sucrose concomitant with decreased polysaccharides might point to a block in their transport rather than from an over production. Kinetin counterbalanced the effects of waterlogging or salinity on photosynthetic activity, probably through more production of enzyme and/or delay of senescence. KEYWORDS – Carbohydrates, photosynthetic activity, salinity, Vigna sinensis;, waterlogging, Zea mays Growth and distribution of plants are controlled chiefly by too little or too much water. Expansive growth is an overriding physiological event, which can be considered as the combined result of the influence of the envir- onmental and metabolic events on the overall plant productivity. Water stress, induced either by waterlogging or salinization affects practically every aspect of plant growth. Photosynthesis is an important process, which can be altered by waterlogging or salinity stress. A decrease in CO 2 assimilation was induced by water- logging (Younis et al., 1993; Habib-ur-Rehman, 1999) and salinity (Sultana et al., 1999). Photosynthetic pigm- ents and certain enzymes are important in driving photo- synthesis. Of these enzymes ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) being the most essential one. Rubisco is by far the most abundant protein present