The Pleiotropic mutant R50 (sym16): A link between cytokinin and starch metabolism may explain its seed phenotype

Cytokinins are a class of adenine-based plant hormones that stimulate cell divisions and are therefore essential for organ growth and development. The role that cytokinin plays in nodulation and that of R50 ( sym16) in particular is very complex. In this study, a cytokinin antagonist and a cytokinin oxidase (CKX) inhibitor were used as tools to study the effects of cytokinin perception or cytokinin degradation on nodulation in pea; the cytokinin transduction pathway, especially that induced by CRE1/AHK4, and CKX playa significant role in pea nodulation. Comparison of the full length sequences PsCKX2 cDNAs from Sparkle and R50 indicated that PsCKX2 is likely not sym16. The availability of the full length PsCKX2 cDNA facilitated the assessment of PsCKX1 and PsCKX2 expression profiles in seedling development using semi-quantitative RT-PCR. Along with a morphological study (dry weight of R50 cotyledons are not decreasing as fast as those of wild type) and microscopic studies (R50 starch grains within the cotyledons are not digested as fast as those of wild type) of seedling development, a working model which integrates cytokinin and starch metabolism is proposed to explain the seedling phenotype of R50.