FREEZING TOLERANCE, PROTEIN-COMPOSITION, AND ABSCISIC-ACID LOCALIZATION AND CONTENT OF PEA EPICOTYL, SHOOT, AND ROOT-TISSUE IN RESPONSE TO TEMPERATURE AND WATER-STRESS

The freezing tolerance of many plants, such as pea (Pisum sativum), is increased by exposure to low temperature or abscisic acid treatment, although the physiological basis of this phenomenon is poorly understo od, The freezing tolerance of pea shoot tips, root tips, and epicotyl tissue was tested after cold acclimation at 2 degrees C, dehydration/r ehydration, applications of 10(-4) M abscisic acid (ABA), and deacclim ation at 25 degrees C. Tests were conducted using the cultivar 'Alaska ', an ABA-deficient mutant 'wil', and its 'wild-type', Freezing injury was determined graphically as the temperature that caused 50% injury (T-60) from electrical conductivity. Endogenous ABA was measured using an indirect enzyme-linked immunosorbant assay, and novel proteins wer e detected using 2-dimensional polyacrylamide gel electrophoresis, The maximum decrease in T-50 for root tissue was 1 degrees C for all geno types, regardless of treatment, For 'Alaska' shoot tips and epicotyl t issue, exogenous ABA increased the freezing tolerance by -1.5 to -4.0 degrees C, while cold treatment increased the freezing tolerance by -7 .5 to --14.8 degrees C. Cold treatment increased the freezing toleranc e of shoot tips by -9 and -15 degrees C for 'wil' and 'wild-type', res pectively, Cold acclimation increased endogenous ABA concentrations in 'Alaska' shoot tips and epicotyls 3- to 4-fold, Immunogold labeling i ncreased noticeably in the nucleus and cytoplasm of the epicotyl after 7 d at 2 degrees C and was greatest after 30 d at the time of maximum freezing tolerance and soluble ABA concentration. Cold treatment indu ced the production of seven, three, and two proteins in shoot, epicoty l, and root tissue of 'Alaska', respectively. In 'Alaska' shoot tissue , five out of seven novel proteins accumulated in response to both ABA and cold treatment. However, only a 24 kDa protein was produced in 'w il' and 'wild-type' shoot and epicotyl tissues after cold treatment. A bscisic acid and cold treatment additively increased the freezing tole rance of pea epicotyl and shoot tissues through apparently independent mechanisms that both resulted in the production of a 24 kDa protein.