Internode Length in Pisum: Variation in Response to a Daylength Extension with Incandescent Light

Lines representing a range of internode length and floweringgenotypes in Pisum sativum L. were grown in 8 h of daylightfollowed by either 16 h of darkness or incandescent light. Thestem elongation response index (RI = length in 24 h ÷length in 8 h) was least in the very short internode nana types,which are grossly deficient in gibberellins (GAs), and the verylong internode slender types, which behave as if saturated withGAs. The common tall (genotype Le) and dwarf (le) types (lepartially blocks conversion of GA₂₀ to the active form, GA₁)were all markedly responsive but the peak RI (based on the mostresponsive internode) was less in tall lines (1.79 to 2.78)than in dwarf lines (2.32 to 5.01) and the peak RI tended tooccur about three to four internodes earlier in tall than indwarf lines. The cry⁸ mutation reduced the RI. (Duplicate lengthloci La and Cry are probably concerned with GA reception.) Amongle dwarf lines, genotype La cry⁸, was generally less responsivethan La Cry, La cry^c and la Cry. Data from crosses showed thaton either an le La or le la background cry⁸ segregates had alower RI than cry⁸ segregates. On an le la background, cry⁸plants were shorter than cry^c plants, cry⁸ was partially dominantto cry⁸ and segregation was clear only in long days. On an lela background, cry^c plants were shorter than cry^c plants, cry⁸was partially dominant to cry⁸ and segregation was clear inlong or short days. The very high peak RI (5.0) of the microcryptodwarfline, L57, appeared to result, in part, from a marked foreshorteningof internodes 4 to 10 in the 8 h regime. In the 24 h regimeL57 (lm) had a fairly similar growth pattern to normal (Lm)cryptodwarf types. The peak RI tended to occur at a lower internode in early thanlate flowering lines, especially among dwarf types, and genotypeswith a day neutral flowering habit (genotype sn or dne) wereless responsive than their photoperiodic counterparts (Sn Dne). White fluorescent light, given as a daylength extension, wasmuch less effective than incandescent light at stimulating stemelongation suggesting control through the phytochrome equilibrium(P_tr/P_total). Pisum sativum, garden pea, daylength extension, flowering, genotype, gibberellin, hormone receptor, incandescent light, internode length, phytochrome, stem elongation