Interaction of phytochromes A and B in the control of de-etiolation and flowering in pea

The interactions of phytochrome A (phyA) and phytochrome B (phyB) in the photocontrol of vegetative and reproductive development in pea have been investigated using null mutants for each phytochrome. White-light-grown phyA phyB double mutant plants show severely impaired de-etiolation both at the seedling stage and later in development, with a reduced rate of leaf production and swollen, twisted internodes, and enlarged cells in all stem tissues. PhyA and phyB act in a highly redundant manner to control de-etiolation under continuous, high-irradiance red light. The phyA phyB double mutant shows no significant residual phytochrome responses for either de-etiolation or shade-avoidance, but undergoes partial de-etiolation in blue light. PhyB is shown to inhibit flowering under both long and short photoperiods and this inhibition is required for expression of the promotive effect of phyA. PhyA is solely responsible for the promotion of flowering by night-breaks with white light, whereas phyB appears to play a major role in detection of light quality in end-of-day light treatments, night breaks and day extensions. Finally, the inhibitory effect of phyB is not graft-transmissible, suggesting that phyB acts in a different manner and after phyA in the control of flower induction.     

The Cultural Keystone Concept: Insights from Ecological Anthropology

The concept of the keystone species has a long history in ecological analysis, although its validity remains controversial. Anthropological researchers have recently coined the term cultural keystone species, but have not demonstrated any significant differences from existing treatments of culturally important species. We define cultural keystones according to their systemic function, as having essential roles in maintaining any level of complexity within a social–ecological system. Examples include bitter cassava consumption among lowland South American groups such as the Wapishana in Guyana, and commercial cultivation of carrots in Rurukan Village in Minahasa, Indonesia. These examples are both essential at one level of systemic reproduction: within the domestic and village economy in the cassava case, and carrots within regional markets. While each is centred upon a single biological species, the cultural keystone itself is not this species, but a complex incorporating several material and non-material system elements.