Reciprocal regulation of Ca²+-activated outward K+ channels of Pyrus pyrifolia pollen by heme and carbon monoxide.

• The regulation of plant potassium (K+) channels has been extensively studied in various systems. However, the mechanism of their regulation in the pollen tube is unclear. • In this study, the effects of heme and carbon monoxide (CO) on the outward K+ (K+(out)) channel in pear (Pyrus pyrifolia) pollen tube protoplasts were characterized using a patch-clamp technique. • Heme (1 µM) decreased the probability of K+(out) channel opening without affecting the unitary conductance, but this inhibition disappeared when heme was co-applied with 10 µM intracellular free Ca²+. Conversely, exposure to heme in the presence of NADPH increased channel activity. However, with tin protoporphyrin IX treatment, which inhibits hemeoxygenase activity, the inhibition of the K+(out) channel by heme occurred even in the presence of NADPH. CO, a product of heme catabolism by hemeoxygenase, activates the K+(out) channel in pollen tube protoplasts in a dose-dependent manner. The current induced by CO was inhibited by the K+ channel inhibitor tetraethylammonium. • These data indicate a role of heme and CO in reciprocal regulation of the K+(out) channel in pear pollen tubes.

Self-compatibility of 'Katy' apricot (Prunus armeniaca L.) is associated with pollen-part mutations.

Apricot (Prunus armeniaca L.) cultivars originated in China display a typical S-RNase-based gametophytic self-incompatibility (GSI). 'Katy', a natural self-compatible cultivar belonging to the European ecotype group, was used as a useful material for breeding new cultivars with high frequency of self-compatibility by hybridizing with Chinese native cultivars. In this work, the pollen-S genes (S-haplotype-specific F-box gene, or SFB gene) of 'Katy' were first identified as SFB1 and SFB (8), and the S-genotype was determined as S1 S8. Genetic analysis of 'Katy' progenies under controlled pollination revealed that the stylar S1-RNase and S8-RNase have a normal function in rejecting wild-type pollen with the same S-haplotype, while the pollen grains carrying either the SFB1 or the SFB8 gene are both able to overcome the incompatibility barrier. However, the observed segregation ratios of the S-genotype did not fit the expected ratios under the assumption that the pollen-part mutations are linked to the S-locus. Moreover, alterations in the SFB1 and SFB8 genes and pollen-S duplications were not detected. These results indicated that the breakdown of SI in 'Katy' occurred in pollen, and other factors not linked to the S-locus, which caused a loss of pollen S-activity. These findings support a hypothesis that modifying factors other than the S-locus are required for GSI in apricot.