No abstract

Abscisic acid inhibits stomatal opening in isolated abaxial epidermal strips of Vicia faba. Kinetin, benzyladenine, and gibberellic acid, which can enhance stomatal apertures in intact leaves, are ineffective on isolated epidermal strips. Abscisic acid appears to act directly on the guard cells, rather than by influencing water potentials throughout the leaf.

No abstract

No abstract

The effect of lght and CO2 on both the endogenous and I-aminocyclopropane-l-carboxyHc acid (ACC)-dep t ethylene evolution from metaboically active detached leaves and leaf discs of Gonphrena globosa L. is reported. Treatment with varying concentrations of ACC did not appear to inhibit photosynthesis, respiration, or stomatal behavior. In all treatments, more ethylene was released into a closed flask from ACC-treated tissue, but the pattern of ethylene release with respect to light/dark/CO2 treatments was the same.Leaf tissue in the lght with a source of CO2 sufflcient to maintain photosynthesis always generates 3 to 4 times more ethylene than tissue in the dark. Conversely, the lowest rate of ethylene release occurs when leaf tissue is lhnminated and photosynthetic activity depletes the CO2 to the compeWsation point. Ethylene rekse in the dark is also stimulated by CO, either added to the flask as bicarbonate or generated by dark respiration. Ethykne release Increases dramaticaly and In parallel with photosyntheis at increasing lght intensities in this C4 plant. Ethylene release appears dependent on CO2 both in the lit and in the dark. Therefore, it is suggested that the Important factor regulating the evolution of ethylene gas from leaves of Gomphrena may be CO2 metabolism rather than ligt per se.Recently, there has been a growing interest in ethylene metabolism in leaf tissue (4,7,8,11,(13)(14)(15)(16)(17)24). However, it appears that whereas there have been attempts to relate ethylene metabolism and action to the metabolism of the leaf in the light, the primary role of photosynthesis itself in regulating carbon flow within the tissue is often ignored. Ethylene is viewed in the literature as a key growth regulator (1), but it must always be remembered (14) that the amount of carbon flowing through ethylene pathways in leaves is very small (pmol carbon mg-' Chl h-') compared with the flux of carbon through photosynthesis, photorespiration, and dark respiration pathways (,umol carbon mg 1 Chl h-'). Several groups suggest that light inhibits ethylene production in leaves because the rate of ethylene release is less in the light than in the dark (7,11,24). We have shown that the conclusion that light is an inhibitor of ethylene production is inconsistent with data obtained when leaf tissue is illuminated and an attempt is made to maintain CO2 levels within the experimental system above the compensation point during the time in which the ethylene determinations are made (14,15 that the major inhibitory effect on ethylene metabolism in leaves attributed to light is a low CO2 effect mediated by the balance of photosynthetic and respiratory activity within the tissue (14). Effects of CO2 on ethylene metabolism in plant tissues other than leaves are well documented (1, 6, 25). We are unaware of any data which show that in leaves it is only ethylene biosynthesis from precursors such as ACC3 (25) which is markedly affected by light and/or C02 in vivo. Therefore, we argue that at this stage of our understanding of...