While at 15/13 ◦C the lateral root length was more closely related to plant DW (r2 = 0.75*** versus 0.23), at 24/20 ◦C the axile root length was more closely related to the plant DW (r2 = 0.46** versus 0.06). The length of the primary lateral roots (PrLat) and the portion of the primary root on the embryonic root system expressed constitutively (Fig. 4e and f) and were related to ΦPSII and SPAD values at low but not at high temperature (Fig. 4a–d). Due to the constitutive expression of the primary root structure, its relationship to photosynthesis at low temperature was largely independent of the temperature at which the roots developed. The variability in primary root structure at 24/20 ◦C explained 16–24% of the variability in
photosynthesis-related traits at 15/13 ◦C (Fig. 4).