Effects of Photoperiod on Growth Rate and Endogenous Gibberellins in the Long-Day Rosette Plant Spinach

Abstract

The earliest visible responses of spinach plants (Spinacia oleracea L., cv. Savoy Hybrid 612) transferred from short to long days (8 hours of high intensity light supplemented with 16 hours of low intensity illumination from incandescent lamps) were upright leaf orientation and increased elongation of the petioles. The effect of long days on growth rate was direct; i.e., there was no after-effect if the plants were transferred to short days. Gibberellin A3 applied to plants under short days had an effect similar to that of long days, whereas application of the growth retardant AMO-1618 [2'-isopropyl-4'-(trimethylammonium chloride)-5'-methylphenyl piperidine-I-carboxylate] under long days caused a growth habit typical of short-day conditions. Gibberellin A3 caused more stem growth in plants under long days in which the endogenous gibberellin content had been reduced by AMO-1618 than in plants under short days not treated with the growth retardant.Three gibberellin-like substances, called I, II, and III in order of increasing RF value, were present in acidic extracts of spinach under short days. After transfer to long days, II increased, whereas I and III decreased, the latter below the level of detection in the d5 corn assay. Following application of AMO-1618 the gibberellin content of plants under long days fell off more rapidly than in those under short days, indicating that gibberellin turnover was markedly higher under long days. This increased rate of gibberellin metabolism was established after 2 long days. When plants were returned to short days, the turnover of gibberellins declined. It is suggested that a higher rate of gibberellin biosynthesis combined with increased sensitivity to gibberellin is responsible for the observed growth responses in spinach under long days.In many rosette LDP,1 application of GA under SD conditions causes stem elongation and flower formation (4, 11, 26). These observations have led to the idea that rosette plants on SD are deficient in GAs, while LD would raise the level of endogenous GAs which in turn would stimulate stem growth e.g., Ref. crease over the SD control by more than a factor of 2. However, results of diffusion experiments suggested that just prior to the onset of stem elongation both the biosynthesis of GA and its metabolism had increased.Working with spinach, Radley (16) reported a sharp although transient increase in GA content after 1 LD. She suggested that the decrease in GA level after more LD cycles was due to greatly increased turnover of GA. In view of this marked increase in the GA content after 1 LD, the levels of native GAs in spinach have been reinvestigated under different photoperiods, as well as the decrease in GA content following the application of the growth retardant AMO-1618. The results in this communication provide experimental support for the notion that the turnover of GAs in spinach is much higher under LD than under SD conditions. Preliminary reports of this investigation have been presented earlier (26, 27). MATERIALS AND METH...

ent-Kaurene Biosynthesis Is Enhanced by Long Photoperiods in the Long-Day Plants Spinacia oleracea L. and Agrostemma githago L

“…The high rates of ent-kaurene synthesis in petioles suggest that these organs may be an important site of GA biosynthesis. This is not unexpected, because petioles of spinach show a rapid a n d large growth response in LD conditions prior to the onset of stem growth (Zeevaart, 1971). In the present experiments, this growth response was inhibited by tetcyclacis.…”

“…Although smaller in magnitude, mature leaves under LD conditions also accumulated more ent-kaurene than those in SD. When spinach plants were treated with tetcyclacis from the onset of LD treatment, petiole and stem elongation were inhibited and the plants continued to exhibit a SD growth habit (Zeevaart, 1971). Petioles that were approximately 0.5 cm long when the plants were transferred to LD conditions had elongated to 6.4 f 0.3 cm (average f SE) after 7 long days, whereas in comparable plants treated with tetcyclacis, the petioles were 1.0 f 0.1 cm long.…”

“…Petiole and stem elongation cease when spinach plants are returned from LD to SD conditions (Zeevaart, 1971). It was of interest, therefore, to determine whether this cessation of growth is correlated with a decreased rate of ent-kaurene biosynthesis.…”

“…In spinach, the photoperiod is known to regulate at least two steps in GA metabolism, namely, the conversion of GAS3 to GA44 and of GAI9 to GAZ0 (Gilmour et al, 1986;Zeevaart et al, 1990;Talon et al, 1991b). Furthermore, L3H]GAZo was metabolized more rapidly in spinach plants in LD than in SD conditions (Metzger and Zeevaart, 1982), and treatment with a growth retardant led to a more rapid decline of the GA content of spinach in LD than in SD conditions (Zeevaart, 1971(Zeevaart, , 1974. Enhanced GA biosynthesis at the later steps of the pathway implies more rapid tumover of precursors earlier in the pathway.…”

Indução do florescimento de Hemerocallis hybrida cv. Graziela Barroso pela aplicação de ácido giberélico

“…De todos os reguladores vegetais que têm sido aplicados em plantas sob condições não indutivas, apenas as giberelinas (GAs) têm demonstrado causar efetiva formação de flores numa grande variedade de espécies (ZEEVART, 1971).…”