Growth analysis of wild-type and photomorphogenic-mutant tomato plants

A custom designed growth-measuring apparatus, controlled by a microcomputer has been used to study extension growth kinetics of wild-type and photomorphogenic-mutant tomato (Lycopersicon esculentum Mill.) plants with. and without end-of-day far-red light (EODFR). The following photomorphogenic mutants were used. Far-red insensitive (fri(1)): deficient in phytochrome A (phyA); temporarily red light-insensitive (tri(3)): deficient in phytochrome B1 (phyB1), and their isogenic wild type (WT) cv. MoneyMaker. aurea (au): deficient in phytochrome chromophore biosynthesis; high-pigment-1 (hp-l): exhibiting exaggerated phytochrome responses, and their isogenic WT cv. Ailsa Craig. The stem elongation rate (SER) during a 24-h period of all the genotypes studied shows a similar pattern, having two dramatic transients, one shortly after the onset of the light period (a sharp decline in SER) and another shortly after the start of the dark period (a sharp increase in SER). These transients are probably associated with water relations as a consequence of opening and closure of the stomata The fastest SER occurs during the dramatic oscillations early in the dark period. Between the genotypes there are large quantitative differences in SER. All the genotypes tested exhibited a strong EODFR response, resulting in a relative promotion of SER during the first period after the start of EODFR and in the subsequent light and dark periods. These results indicate that phyA, absent in the fri(1) mutant, does not play a major role in SER of light-grown tomato plants, whereas phyB1, absent in the tri(3) mutant, is partly responsible for the compact stature of WT plants. An additional phytochrome other than phyA and phyB1 must therefore be capable of eliciting the EODFR response.