Submitted to: Plant Biology
Publication Type: Abstract Only
Publication Acceptance Date: July 21, 2001
Publication Date: N/A
Technical Abstract: The influence of prolonged drought-induced water stress on the steady- state levels of ascorbic acid (ASC), dehydroascorbate (DHA) and the ASC:DHA redox status in leaves of Glycine max (soybean) was examined. Two soybean cultivars (cv Essex and cv Forrest) were grown in high light growth chambers (1000-1200 umol photons per square meter per sec) or in the greenhouse during May, June, and July 1999. The cultivars were supplied with water until 25-29 days post-emergence at which time one half of the plants were not watered for 4.5 to as long as 7.5 days; the other half of the plants were provided water daily and served as controls. On designated days, leaf water potential was measured and leaf disks of constant area were excised in the period between 1230 and 1330 hrs. Leaf disk samples were immediately frozen in liquid nitrogen; leaves were extracted and ASC and DHA levels were measured and expressed as umol per gm dry mass per time point. Low leaf water potential values (-3.00 to - 3.95 megapascals) in both cultivars were accompanied by slight decreases in ASC levels and slight increases in DHA levels per gm dry mass. In some cases, leaf ASC levels of water-stressed plants were similar to controls or were even increased by as much as 1.2 times. The mole fraction of leaf ASC remained at 93 to 99 mol % of the total ascorbate (ASC+DHA) indicating that most of the total ascorbate remained in the reduced form even at low water potential. It is concluded that during water stress, enzymes of the ascorbate-glutathione cycle in leaf mesophyll cells, as well as the system that generates reductant to support DHA to ASC recycling, e.g. photosynthetic electron transport in chloroplasts, is able to remain active enough to maintain reduction of DHA to ASC.