Abstract:
The innate ability of potato leaf tissue to initiate freezing
was studied. Two potato species, the non-hardy cultivated potato
Solanum tuberosum L. cv. Russet Burbank, and Solanum acaule Bitt. a
hardy species from South America, were studied. Two treatments,
low (cold) and high (warm) temperatures were included to study the
effects of growing environment on ice nucleation activity. The
nucleation characteristics of cell suspensions, leaf disks and
leaflets were determined.
A procedure was developed to isolate and purify mesophyll
cell suspensions from potato leaves prior to testing of the cell
suspensions. This procedure involved the use of clear adhesive
tape attached to the upper and lower epidermis during enzymatic
degradation. The tape held the epidermis together allowing its
removal and exclusion from the resulting suspension. Mesophyll
cell suspensions prepared in this way contained less than 11%
epidermal cells.
Data from droplet freezing assays of suspensions and leaf
disks were plotted as percent frozen vs. temperature. No
substantial nucleation activity occurred above -9°C. Nucleation
activity for suspensions was lower than leaf disks.
The temperature of ice formation in leaflets was determined
by differential thermal analysis (DTA). Mean temperatures of
freezing were -11.1 and -12.1°C for S. acaule warm and cold
respectively, and -11.4 and -9.9°C for S. tuberosum warm and cold.
There are no significant differences between means at the 5% level.
Plant hardiness was determined by whole plant freezing. Cold
grown S. acaule survived -6°C while warm grown S. acaule survived
-4°C. S. tuberosum only tolerated -2°C for the warm and -2.5°C
after a cold treatment.
The differences between plant hardiness and leaf nucleation
temperatures indicate that intrinsic leaf ice nucleators do not
substantially limit supercooling in potato.
