EFFECTS OF DROUGHT STRESS ON DRY-MATTER P RODUCTION, PARTITIONING ANDHISTOLOGICAL CHARACTERISTICS IN SOYBEAN

In previous publications, we have shown that the stomatal morphogenesi s, stomatal movement, photosynthesis, and osmotic adjustment of soybea n plants were affected by long-term draught treatment. In this study, six soybean varieties, i.e., Dah liarn, Wakashima, Native 13, AGS 62, Sanluis, and 66-F-4-2 were cultivated with an automatic PVF water cont rol system and the structure of the shoot, dry matter production and p artitioning were investigated. Under severe drought stress, the biomas s, leaf area, specific leaf weight, and the partitioning of dry matter in pods were reduced obviously. The degrees of reduction were differe nt among varieties and were related to their drought resistance. That is, the drought stress has less effects on the high drought-resistant variety AGS 62 and has profound effects on the drought-sensitive varie ty Native 13. Under drought stress, mesophyll cell became shorter and more compact, cell numbers increased on a leaflet area basis. Intercel lular air space therefore was reduced from 45% of the non-stressed pla nt to 30% of the stressed plant. The total intercellular air space of mesophyll was positively correlated with photosynthetic rate and leaf conductance. The correlative coefficients were 0.896(**) and 0.898(** ), respectively. This results indicated that the change of intercellu lar air space of mesophyll was closely related with air diffusion resi stance. Under drought stress, shoot vascular tissues became smaller, v essel also became narrower. The growth and differentiation of vascular tissues were obviously inhibited. It showed that responses of vascula r growth and differentiation to drought stress were different among va rieties and were related to their drought resistance. Under drought st ress, shoot vascular tissues became smaller, vessel also became narrow er. The growth and differentiation of vascular tissues were obviously inhibited. It showed that responses of vascular growth and differentia tion to drought stress were different among varieties and were related to their drought resistance.