An Investigation into the Stomatal Behaviour of a Wilty Mutant of Pisum sativum

The water relations and stomatal behaviour of a wilty line ofpea (JI 1069) were investigated and compared with those of severalnon-wilty lines (JI 1180, JI 1194, and JI 74). The leaves ofthe wilty line were found to have a lower percent water content,water potential and diffusive resistance and the dimensionsof the stomatal cells were larger than those of the non-wiltytypes. The aperture of stomata on epidermal samples taken from plantsin the light or dark period of a diurnal rhythm was consistentlylarger for the wilty pea than for the non-wilty lines, however,their stomatal responses on detached epidermis to light, CO₂and KC1 concentration were similar. There was no differencein response to ABA of stomata on detached epidermis of wiltyor non-wilty types of pea. Key words: Pisum sativum, Wilty mutant, Water relations, Stomatal behaviour     

Changes in starch and glucose levels in the epidermis of Commelina communis in relation to stomatal movements

Abstract Starch levels in Commelina communis epidermis, were shown to be higher in the dark than in the light, from plants kept under an imposed photoperiodic regime. These changes were also inversely correlated with diffusive conductance (1/diffusive resistance, 1 /R) of the leaves used. Even after advancing the photoperiod by 7 h the changes in starch levels continued for at least 1 d and were still inversely correlated with 1/R. Corresponding changes in glucose levels were measured in the same tissue and were found to correlate with 1/R at the end of the dark period and mid photoperiod, but not at the beginning of the dark period. These changes are discussed in relation to possible mechanisms of stomatal opening and closing.     

Studies on the Properties of Carboxylating Enzymes in the Epidermis of Commelina communis

A spectrophotometric assay has been used to measure the activityof PEP carboxylase and RuBP carboxylase in the epidermal andmesophyll tissue of Commelina communis. On both a chlorophylland protein basis the PEP carboxylase activity was always greaterin the epidermis than in the mesophyll, whereas RuBP carboxylaseactivity was always highest in the mesophyll. PEP carboxylaseactivity in epidermal extracts was lost very slowly and itspH optimum was a broad one in the range 7·5–8·0.The K_m values for PEP carboxylase in the epidermis and mesophyllobtained from light- and dark-treated plants were not very differentalthough its V_max was much lower in dark-treated tissue. Thesedata are discussed in relation to the possible role of PEP carboxylasein guard cell metabolism.     

The Physiology of a Wilty Pea: Abscisic Acid Production under Water Stress

‘Wilty’ (JI 1069), a mutant of Pisum sativum, hasbeen examined for its ability to produce abscisic acid (ABA)under water stress. ABA was measured using combined gas chromatography-massspectrometry and multiple-ion-monitoring employing a deuteratedinternal standard. In intact droughted plants, ‘Wilty’produced less ABA than a non-wilty line (JI 1194) and maximumproduction was delayed. Detached leaves of the wilty mutantlost significantly more water than control leaves but did notshow an increase in ABA content. Non-stressed mutant materialfrom both intact plants and isolated leaves contained less ABAthan control tissue. Key words: Pea, Wilty mutant, Abscisic acid