Development of Freezing Tolerance in Leaves of C₄ Grasses

Abstract

The rate of development of freezing tolerance in the leaves of 11 C₄-photosynthetic pathway grasses growing outdoors at Palmerston North (40° 23′S., 175 37′E.) in field plots was measured during autumn and winter. The leaves of two species only, Paspalum dilatatum and Eragrostis curvula, increased markedly in freezing tolerance and survived frosts in mid-winter. To simulate autumn and winter conditions, temperature and daylength were decreased gradually in a controlled-environment growth cabinet. Leaves of P. dilatatum grown in this cabinet showed similar changes in freezing tolerance to leaves grown outdoors in autumn and winter. The temperature at which leaves were severely damaged decreased from - 3.4°C to - 8.9°C. Expanding leaves responded to the current hardening temperature, but little increase in freezing tolerance occurred in leaves exposed to the hardening temperature once their growth was completed.