Cold Hardiness and Peroxide Metabolism in the Genus Malus in Midwinter

Abstract

To clarify the biochemical mechanism of differences in cold hardiness among woody species, the degree of cold hardiness and the activities of enzymes related to peroxide-producing systems and peroxide-scavenging systems were compared among 9 species containing 3 cultivars of the genus Malus in midwinter.
1. The twigs of the genus Malus could be divided into four classes with respect to cold hardiness as follows:
Tender; M. pumila Mill. var. domestica Schneid. cv. Jonathan, M halliana Koehne
Moderately tender; M. pumila Mill. var. domestica Schneid. cv. Delicious, M. asiatica Nakai
Moderately hardy; M. pumila Mill. var. domestica Schneid. cv. McIntosh,
M. prunifolia Borkh. var. ringo Asami, M. sieboldii Rehd.,
M. sieboldii Rehd. var. arborescens, M. platycarpa Rehd.
Hardy; M baccata Borkh., M. astracanica Dum.
2. In the living bark and xylem of twig of the genus Malus in midwinter, the activities of enzymes related to the peroxide-scavenging systems were higher in M. pumila var. domestica (3 cultivars), M astracanica, M asiatica and M. baccata than in other species tested. A similar result was also observed in the activities of NADH-Cyt c reductase (NADH-CcR) and Cyt c oxidase (CcO), enzymes that are related to the peroxide-producing systems. With some exceptions, the activities of enzymes in the peroxide-scavenging systems showed a significant degree of correlation with the activities of NADH-CcR or CcO. High correlation coefficients were obtained between the activities of glucose-6-phosphate dehydrogenase (G6PDH) and the activities of NADH-CcR (living bark, r= +0.944**; xylem, r= +0.877**) and CcO (living bark, r= +0.973**; xylem, r= +0.937**).
3. The ratio of the activity of NADH-CcR to that of G6PDH or of CcO activity to that of G6PDH was defined as the index of cellular status that represented susceptibility to oxidation stress (oxidizability index, OI) and the relationship between the values of OI and the cold hardiness of twigs was investigated. No relationship was found between the cold hardiness of twigs and the values of OI in the living bark. However, the cold hardiness of twigs showed a significant negative correlation with the ratio of the activity of NADH-CcR to that of G6PDH (r= -0.793**) and with that of the activity of CcO to the activity of G6PDH (r= -0.662*) in the xylem. Thus, the cold hardiness of twigs in the species and cultivars examined decreases with an increase in the values of OI in the xylem.
From these results, it appears that the cold hardiness of twigs of the genus Malus in midwinter is closely related to the peroxide metabolism in the xylem.