Ultrastructural Differences in Leaf Cells of Some Solanum Species in Relation to Their Frost Resistance

Ultrathin sectioning techniques and morphometric measurements were used to study the ultrastructural differences between Solanum acaule, a frost-resistant potato species, and S. tuberosum `Red Pontiac,' a frost-susceptible cultivar, which had been grown under long-day and warm-temperature conditions and also under cold-acclimating environmental conditions. In general, under long-day and warm-temperature conditions, the cell wall of S. acaule is about twice as thick as that of S. tuberosum `Red Pontiac,' and the number of osmiophilic globuli in the chloroplasts of S. acaule is also much higher than that in S. tuberosum `Red Pontiac.' After cold-acclimating treatments, the chloroplasts of S. acaule, which can be cold acclimated, appeared to change very dramatically while the chloroplasts of S. tuberosum `Red Pontiac,' which cannot be cold acclimated, did not change significantly. The increase in the number of osmiophilic globuli and the disappearance of starch grains in the chloroplasts were associated with the development of frost hardiness in the leaf cells of S. acaule.