Involvement of phytochrome B in DIF mediated growth in cucumber

This study aimed to compare the interaction between light quality and alternating day (DT) and night temperature (NT) under two different daily light integrals (DLI) on morphology of a wild type (wt) and a phytochrome B deficient mutant (lh) of cucumber (Cucumis sativus L.). Different light qualities were established by light quality selective plastic films. Plants were grown for 18 days (lh) or 19 days (wt) under DT/NT regimes of 25/19 °C (positive DIF), 22/22 °C and 19/25 °C (negative DIF) (12-h thermoperiod) in combination with plastic films establishing a low (0.75, LRFR) and high red (R)/far-red (FR) ratio (1.62, HRFR) and a control (R/FR of 1.11). Stem, hypocotyl and internode elongation in the wt were more affected by DIF under LRFR than HRFR. In general, length was reduced 45–50% under HRFR compared to the control, while the reduction by negative DIF was 38% on average. Hypocotyl length of the lh mutant was neither affected by temperature regime nor light quality, while negative DIF reduced stem length with 15–20% compared to positive DIF due to a delayed internode elongation. The general response pattern in both genotypes was not affected by an additional reduction in DLI of 50%. In conclusion, the strongest effect of DIF was found under a LRFR which is the opposite of findings in earlier studies with day extentions with different light qualities. In general, HRFR reduced stem elongation of cucumber more than negative DIF. The results indicate a crosstalk between light phytochrome responses and thermoperidism.