Changes in photosynthesis, dark respiration rates and photosynthetic carbon partitioning in winter rye and wheat seedlings during cold hardening

In order to elucidate whether there is any correlation between freezing tolerance of plants and some parameters characterizing their source-sink relations at: different levels of plant structural organization, a number of certain responses of winter rye and wheat seedlings to cold hardening was determined. It has been found that in both crops the ratio of light-saturated photosynthesis rate to that of dark respiration increased about 2-3-fold after hardening while the initial difference in the value of this parameter (it was higher by about 40 % in rye seedlings as compared with that in wheat seedlings) was kept. In addition, cold hardening of both crops resulted in a marked increase in the contents of sugars, lipids and cytoplasmic proteins in leaf tissues, in the ratios of high-mol.-wr. polypeptide content to that of low-mol.-wt. ones, of membrane lipid content to that of membrane proteins, of phospholipid content to that of sterols, of unsaturated fatty acid content to that of saturated ones, of relative cross-section area of chloroplasts to that of a single cell and of the same area of plastoglobules to that of a single chloroplast. These results suggest that the changes observed in the above parameters reflect the development of additional assimilate sinks at various levels of plant structural organization to maintain a sufficiently high rate of photosynthesis at low temperature. According to the data obtained, under these conditions rye seedlings develop a higher sink capacity than wheat seedlings and for this reason likely exhibit more effective frost adaptation as compared with that of the latter crop.