A MUTANT-BASED APPROACH, USING PISUM-SATIVUM, TO UNDERSTANDING PLANT-GROWTH

The benefits of a mutant-based approach to the examination of elongation growth are Outlined. In Pisum sativum L. 15 mutants have been isolated that modify elongation and multiple alleles have been identified at nine of these loci. Using appropriate screening techniques these mutants have been shown to modify growth in a wide range of ways. Four mutants, le, na, lh, and ls, block the synthesis of GA1 while s/n increases GA1 levels by blocking GA-catabolism. Two mutants, lv and lw, are classified as photomorphogenic mutants. While lv lacks responses attributable to phytochrome B, lw displays an enhanced response to phytochrome. Several mutants lacking a normal response to GA1 have been identified and include lk, lka, lkb, lkc, lkd, and la cry(s). The mutations lka and lkb alter the chemorheological properties of the cell wall and result in increases in the wall-yield threshold and turgor pressure while la and cry(s) may act at, or close to, the point of reception of the GA1 signal. The role of auxin in elongation of intact plants is currently being examined using these mutants since some modify IAA levels (e.g., lkb, lv). Other growth processes are also influenced by many of these mutants. Leaf growth is examined as an example of how mutants of known effect (e.g., dwarf, GA biosynthesis mutants) may be used to determine the role of hormones in other related developmental processes.