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During stomatal opening potassium uptake into guard cells and [K.sup.+] channel activation is tightly coupled to proton extrusion. The pH sensor of the [K.sup.+] uptake channel in these motor cells has, however, not yet been identified. Electrophysiological investigations on the voltage-gated, inward rectifying [K.sup.+] channel in guard cell protoplasts from Solanum tuberosum (KSTI), and the kst1 gene product expressed in Xenopus oocytes revealed that pH dependence is an intrinsic property of the channel protein. Whereas extracellular acidification resulted in a shift of the voltage-dependence toward less negative voltages, the single-channel conductance was pH-insensitive. Mutational analysis allowed us to relate this acid activation to both extracellular histidines in KST1. One histidine is located within the linker between the trans-membrane helices S3 and S4 (H160), and the other within the putative pore-forming region P between S5 and S6 (H271). When both histidines were substituted by alanines the double mutant completely lost its pH sensitivity. Among the single mutants, replacement of the pore histidine, which is highly conserved in plant [K.sup.+] channels, increased or even inverted the pH sensitivity of KST1. From our molecular and biophysical analyses we conclude that both extracellular sites are part of the pH sensor in plant [K.sup.+] uptake channels.

Conidiophore development in Neurospora crassa is influenced by illumination. The expression of two con genes, con-5 and con-10, the blue light-inducible gene bli-4 and al-1 and al-2, which are expressed during conidiation and are light-inducible, were investigated. The results showed that these photoregulated genes are also regulated by nitrogen limitation. In addition, experiments on two nonphotoresponsive strains, wc-1 and wc-2, showed that the activity of the wc gene products are not required in nitrogen regulation.

Investigates the regulatory networks in stomatal guard cells through a molecular genetic approach. Gene encoding proteins and its importance to guard cell functions; Effect of environmental factors on the changes in guard cell gene expression; Effect of the AB13 gene on stomatal regulation.