Interrelations Between Photoperiod, Frost Hardiness and Sulfhydryl Groups in Cabbage

Abstract

Cabbage seedlings grown in short days (SD-8 or 12 hr.) and long days (LD- 18 or 24 hr.)were hardened by exposing them successively to +5[degree], 0[degree] -3[degree]C. Soluble protein plus non-protein N showed a net increase only in the SD plants. In both SD and LD plants, it decreased to a minimum toward the end of the 1st stage of hardening, increased to a maximum in the 2nd stage. This degree of change was proportional to photoperiod and mainly due to the proteins. SH content rose during the 1st 1 to 2 weeks, but only in the SD plants. This rise was primarily due to the protein fraction. After the first 1 to 2 weeks both SD and LD plants showed a decrease in SH content, most pronouncedly during the 2nd stage of hardening. Nonprotein SH content was very low and decreased during hardening in both SD and LD plants. Nonprotein SS increased during the 1st stage of hardening. Total nonprotein SH+2SS rose to a maximum during the 1st stage of hardening, paralleling both osmotic potential and hardiness. During the 2nd stage of the total decreased, in spite of the rise in hardiness. These results held true for both SD and LD plants, and are all explainable on the basis of the SH SS theory of frost resistance.