| 'Super-Dwarf' wheat (Triticum aestivum L.) was grown in the Russian Space Station Mir. The plants remained completely vegetative during their entire development, looking like "crabgrass" in the 1995 Greenhouse 2 mission and failing to form seeds in the 1996 NASA-3 mission although the plants grew well and formed many heads. Our experiments simulated several environmental stress factors such as low light level, short photoperiods, water stress, and high CO{dollar}sb2{dollar}, which occurred during the space flight, so that we could study influences of these factors on hormonal levels in plants on the ground. Plants of 'Super-Dwarf' wheat were grown at the following light levels: 1,400 (average noon-time measurement without shading), 400, 200, and 100 {dollar}mu{dollar}mol{dollar}cdot{dollar}m{dollar}sp{lcub}-2{rcub}cdot{dollar}s{dollar}sp{lcub}-1{rcub}{dollar}. At the boot stage, abscisic acid (ABA) in leaves and roots significantly increased in the lower light levels compared with plants in natural light. The cytokinins, zeatin, zeatin riboside, dihydrozeatin, dihydrozeatin riboside, and isopentenyl adenine, did not reach detectable levels in 150 mg dry mass samples of roots and 600 mg dry mass samples of leaves. Indole-3-acetic acid (IAA) accumulated in both roots and leaves after 'Super-Dwarf' wheat plants were grown under low-light. ABA and IAA accumulations in roots might be involved in "signal" transport from leaves to roots. Isopentenyl adenosine (iPA) was assayable in both roots and leaves of 'Super-Dwarf' wheat but did not show any difference among the four light levels.; Long-term exposure to high CO{dollar}sb2{dollar} did not affect ABA accumulation in leaves, but photoperiod was correlated with ABA accumulation in leaves. ABA content in leaves was significantly higher under longer photoperiods compared with shorter photoperiods. ABA, iPA, and IAA in roots and leaves were quantified after the whole root system, half root system, and triad root system of a plant were subjected to water deficit and waterlogging. Water deficit promoted ABA accumulation in both roots and leaves, promoted iPA accumulation in leaves, inhibited iPA accumulation in roots, and inhibited IAA accumulation in both roots and leaves. Waterlogging stimulated a transient increase in ABA, iPA, and IAA. In the half-root-stressed and the triad root systems, the increase in ABA and the decrease in iPA and IAA are correlated with the proportion of roots stressed or waterlogged, which reflects the availability of water. |
