Blue-Light Regulation of Epicotyl Elongation in Pisum sativum

Abstract

Blue light is known to induce suppression of stem elongation. To avoid the complication of blue-light-induced transformation of phytochrome we have adapted the procedure of measuring bluelight-induced suppression of stem elongafton in Pisum sativum L.var Alaska grown under continuous red light. The resulting fluence-response curve for suppression of epicotyl elongation measured twenty-four hours after a blue-light treatment is bellshaped, with the peak of suppression between 100 and 10' micromoles per square meter, and no suppression at 10 micromoles per square meter. Suppression is first observed 5 and 11 hours after the blue-light treatment for the fourth and third internodes, respectively. No significant differences in elongation rates were noted for the 10 micromoles per square meter treated seedlings throughout the 24 hour period. Reciprocity holds for both third and fourth intemodes in response to 101 and 104 micromoles per square meter of blue light over the range of irradiation times tested (100 to 104 seconds, 10' micromoles per square meter; 100 to 103 seconds, 104 micromoles per square meter). In contrast to the bell-shaped fluence-response obtained for epicotyl elongation, measurements of chlorophyll and carotenoid accumulation indicate increasing accumulation with increasing fluence.

Two Distinct Blue-Light Responses Regulate Epicotyl Elongation in Pea

“…The data show that the kinetics for suppression in response to high fluence blue light are identical to those for low fluences; suppression starts between 18 and 24 h after the blue-light treatment. The time at which suppression becomes apparent is similar to that observed for the suppression of the third internode in red-light-grown plants (16).…”

“…The data indicate that suppression occurs with a threshold below 10-' ,umol m-2 and persists through 104 ,umol m-2. This contrasts the lack of suppression observed for red-light-grown plants treated with 104 ,umol m-2 of blue light (16).…”

“…1), but is apparent in red-light-grown plants (16). Two roles can be envisioned for the red light in allowing the blue high fluence response: (a) to ensure that Pfr is present at the time of high fluence blue-light irradiation or (b) to ensure that the plant be in a specific developmental state at the time of high fluence blue-light irradiation.…”

“…Several (2,3,(10)(11)(12). Those responses showing bell-shaped fluence-response characteristics under continuous red-light conditions include phototropic curvature for several monocot and dicot species, including pea (curvature toward a unilateral light source at low fluences, less curvature at higher fluences) (2,3), long-term suppression of epicotyl elongation in pea (suppression at low fluences, alleviation at higher fluences) (16), and control of the steady-state level of Cab2 RNA pEA215 RNA in pea (accumulation at low fluences, return to control levels at high fluences) ( 17).…”

Characterization of a Rapid, Blue Light-Mediated Change in Detectable Phosphorylation of a Plasma Membrane Protein from Etiolated Pea (Pisum sativum L.) Seedlings

“…phototropism, 14), fluence response measurements of the change in detectable phosphorylation in membranes from red-grown peas are similar to those from etiolated plants (data not shown). Warpeha and Kaufman (24) studied inhibition of elongation in red-grown plants 24 h after giving a blue light pulse and found a wider range of active fluences than those for the more rapid inhibition of growth (16) or for the observable change in in vitro phosphorylation.…”