SUMMARYThe effects of several phenolic compounds, some of which accumulate in tissues under the stress of microbial attack, and of some * water-stress' compounds (those which accumulate in leaf tissue under water-stress and may cause stomata to close) on stomatal behaviour in epidermal strips of Commelina communis L. were studied.The phenolics, /)-coumaric acid, caffeic acid, chlorogenic acid, salicylic acid and particularly sinapic acid, were strong inhibitors of stomatal opening. The effects on open stomata were less marked but sinapic acid brought about considerable closure while ferulic acid stimulated wider opening.All the 'water-stress' compounds except proline and glutamine, which had no effect on stomatal behaviour, inhibited opening and caused some closure of initially open stomata; ABA, farnesol, undecanoic acid, linoleic acid and a-linolenic acid were all particularly effective.
SUMMARYThe effects of the phytoalexins, rishitin, pisatin, wyerone acid and phaseollin, (all at 0-1 mol m~^) were tested on stomatal responses in epidermal strips of Commelina communis L. and Viciafaba L. Additionally, the effects of the phytoalexins on guard cell protoplasts of C communis were examined and compared with those of several 'water-stress' compounds namely ahscisic acid (ABA), farnesol, nonanoic and undecanoic acids, and a-linolenic acid. Phytoalexins may be loosely defined as 'microbial stress' compounds while 'water-stress' compounds are defined as those which accumulate in leaf tissue under water-stress and close stomata or act as osmotic adjusters.Wyerone acid and phaseollin inhibited stomatal opening in C. communis to the same extent as ABA, while rishitin had no significant effect and pisatin had an intermediate effect.When stomata were open, treatments with phaseollin and ABA brought about a marked closing response, while those with pisatin and rishitin were not statistically significant from the controls; wyerone acid initially opened stomata further but after 5 h exposure stomatal apertures were similar to those of the controls.Stomatal opening in epidermis of V.faba was greatly inhibited by ABA, while all phytoalexin treatments resulted in intermediate inhibitory effects between those obtained with the control and ABA treatments, wyerone acid being the most inhibitory.Pisatin and rishitin (at 0-1 mol m"^) had no discernible effects on guard cell protoplasts, while phaseollin and wyerone acid (at 0-1 mol m~^) caused loss of protoplast viability. The 'water-stress' compounds, nonanoic, undecanoic and a-linolenic acids, also caused gradual loss of protoplast viability and farnesol caused lysis of protoplasts. Only ABA caused protoplasts to contract without loss of vitality. Thus phaseollin and, to a lesser extent, wyerone acid have similar properties to ABA in that they inhibit stomatal opening and promote closure. However, unlike ABA but like farnesol, nonanoic, undecanoic and a-linolenic acids, their effects are likely to be associated with phytotoxicity, their phytotoxicity depending on duration of exposure and on concentration.
SUMMARYThere are certain features shared by phytoalexins (which can be loosely defined as microbial stress compounds) and water-stress compounds such as ABA. Therefore, a study was made to determine if phytoalexins behaved in a similar fashion to water-stress compounds and in this report phytoalexin accumulation in water-stressed leaves was investigated.Phytoalexins were not detected in mildly water-stressed leaf tissue oi Pisum sativum L. or Vicia faba L. However, if plants were severely water-stressed resulting in damaged and dead areas in their leaves, a fungi toxic substance corresponding to pisatin was detected in the damaged areas of pea leaves and, to a lesser extent, in areas which recovered full turgor, while a number of fungitoxic substances, two of which corresponded to wyerone and wyerone acid, occurred in the damaged and recovered areas of V.faba leaves.Thus, although phytoalexins may accumulate in severely water-stressed leaves they do not apparently behave in a similar manner to water-stress compounds such as ABA which would be expected to accumulate in leaves even under mild water-stress.
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