8.4.4  phy mutants

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Sorting out which phytochrome type is associated with each physiological response has been aided greatly by phytochrome mutants, mostly in Arabidopsis, but also in pea, tomato and sorghum. Some of the mutants have a defective chromophore, others have lesions in the protein part of the molecule. For example, phyB mutants exhibit changes in germination, elongation growth, flowering time and chlorophyll accumu-lation. This suggests that each phytochrome has multiple functions. Some of these processes are also altered in phyA mutants, but often in subtly different ways. We can tentatively conclude that phytochromes interact to orchestrate many aspects of plant development. Smith (1995) has attempted to put all these functions into an ecological context, and has assigned each to a particular class of response (Figure 8.34).


Figure 8.34 Multiple phytochrome sensing systems enable plants to adjust development under a wide range of ecologically important light environments. VLFR = very low fluence response, LFR = low fluence response, HIR = high irradiance response.

(Based on Smith 1995)