Three chemicals, viz., thiourea, thiamine and ascorbic acid capable of potentiating-SH turnover, were tested with the objective to improve growth and productivity of maize. Thiourea was tested as seed-soaking and foliar-applied treatments as also in combination. Thiamine and ascorbic acid were tested as foliar sprays alone. Foliar treatments were applied at vegetative stage (30 and 45 days after sowing).The results of the field experiment showed that seed soaking with thiourea (500 ppm) tended to improve grain yield (13.4 per cent over control), but improvement in biological yield was significant. However, seed soaking plus foliar treatment of thiourea significantly increased both biological and grain yields, besides causing significant improvement in leaf area index and number of green leaves plant"^ The increase in grain yield ha"' was of the order of 34.6 per cent over control.It was further noted that foliar sprays of thiourea (1000 ppm), thiamine (100 ppm) and ascorbic acid (100 ppm) significantly increased leaf area index, number of green leaves plant"^ and biological yield ha~'. These treatments also significantly increased grain yield ha*' by 40.6, 20.2 and 26.3 per cent, respectively over control. Improvement in maize yield with thiourea, thiamine and ascorbic acid treatments appeared to have resulted from increased photosynthetic efficiency and canopy photosynthesis on account of the biological activity of -SH group. It was also apparent that leaf senescence was delayed under the influence of these chemicals. It is therefore suggested that thiourea, thiamine and ascorbic acid are the potential bioregulators for improving photosynthetic efficiency and grain yield of maize and possibly other cereals, and that thiourea, a sulphydryl compound, holds considerable promise in this context.

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Photosystem 1 and 2 and antioxidant enzyme activities were determined in wheat (Triticum aestivum L. cv. Sonalika) leaves. Seedlings from both control seeds and seeds soaked in solutions like dithiothreitol, thioglycollic acid and thiourea were subjected to water stress induced by polyethylene glycol. Photosystem 1 and 2 activities were less inhibited by water stress due to seed soaking with sulphydryl compounds. The changes in activities of antioxidant enzymes induced by water stress were higher in seedlings from thiol-pretreated seeds than from water-soaked seeds.

Three sulphydryl compounds, viz., 2-mercaptoethanol, 2-mercaptoethylamine and thiourea, were tested for improving dry matter partitioning and grain production of maize in field culture. The chemicals were applied ca. 0.1 % concentration as foliar spray at grain formation stage. Mercaptoethanol, mercaptoethylamine and thiourea increased grain yield ha"' by 18.1, 29.2 and 34.1 %, respectively compared with water control Significant improvement in harvest index, a measure of dry matter partitioning for grain production, was also noted with the spray chemicals but stover and biological yields ha"^ remained uninfluenced. Foliar spray of 0.1 % urea did not have any effects on the above parameter and thus the effects of thiourea were largely a function of sulphydryl group. It is suggested that sulphydryl compounds have a considerable potential for increasing grain production of maize and perhaps of similar other cereals.

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