THE INFLUENCE OF TEMPERATURE UPON PHYSIOLOGICAL PROCESSES IN EARLY-FLOWERING AND LATE-FLOWERING STRAINS OF THLASPI-ARVENSE L

This study was initiated to determine net photosynthesis, respiration, and stomatal conductance for early-flowering (EF) and late-flowering (LF) strains of Thlaspi arvense L., and to determine the relative impa ct of temperature on these processes in the two strains. The strains h ave been shown to differ by a single gene. Vernalized EF and LF plants were grown under controlled environments at day temperatures of 15 de grees C, 20 degrees C, and 25 degrees C (16-h photoperiod) each, with 15 degrees C nights. During the period of floral initiation for the EF strain, net photosynthesis, respiration, and stomatal conductance wer e determined in both strains. Plants of the LF strain had higher net p hotosynthesis rates and lower respiration rates. Net photosynthesis wa s most efficient at 20 degrees C days, while respiration rates increas ed with increasing temperature. Stomatal conductance was greater in th e EF strain, which also had Larger stomata than plants of the LF strai n. Generally, EF plants grew more quickly in terms of shoot dry weight than LF plants. However, at 25 degrees C, the LF plants had significa ntly more shoot dry weight. We suggest that differential net photosynt hesis and respiration rates of the EF and LF strains of T. arvense may influence the relative amounts of carbohydrates and nitrogen availabl e to the shoot apices and therefore affect the time to floral transiti on.