Green light reduces elongation when partially replacing sole blue light independently from cryptochrome 1a

Abstract

Although green light is sometimes neglected, it can have several effects on plant growth and development. Green light is probably sensed by cryptochromes (crys), one of the blue light photoreceptor families. The aim of this study is to investigate the possible interaction between green and blue light and the involvement of crys in the green light response of plant photomorphogenesis. We hypothesize that green light effects on morphology only occur when crys are activated by the presence of blue light. Wild-type Moneymaker (MM), cry1a mutant (cry1a), and two CRY2 overexpressing transgenic lines (CRY2-OX3 and CRY2-OX8) of tomato (Solanum lycopersicum) were grown in a climate chamber without or with green light (30 μmol m^-2 s^-1 ) on backgrounds of sole red, sole blue and red/blue mixture, with all treatments having the same photosynthetic photon flux density of 150 μmol m^-2 s^-1 . Green light showed no significant effects on biomass accumulation, nor on leaf characteristics such as leaf area, specific leaf area, and chlorophyll content. However, in all genotypes, green light significantly decreased stem length on a sole blue background, whereas green light hardly affected stem length on sole red and red/blue mixture background. MM, cry1a, and CRY2-OX3/8 plants all exhibited similar responses of stem elongation to green light, indicating that cry1a, and probably cry2, is not involved in this green light effect. We conclude that partially replacing blue light by green light reduces elongation and that this is independent of cry1a.

FIGURE 1

Effect of partially (20%) replacing sole red (R), sole blue (B) or red/blue (RB; ratio 3:1) by green (G) light on the phenotypes of four tomato genotypes: MM (Moneymaker, wild‐type), cry1a (CRY1a‐deficient), CRY2‐OX3 (CRY2 overexpressing, line 52.3), and CRY2‐OX8 (CRY2 overexpressing, line 52.8). A picture of one representative plant is shown per combination of light treatment and genotype

IGURE 2

F Effect of partially (20%) replacing sole red (R), sole blue (B) or red/blue (RB; ratio 3:1) by green (G) light on stem length on day 21 after transplanting of four tomato genotypes, (A) MM (Moneymaker, wild‐type), (B) cry1a (CRY1a‐deficient), (C) CRY2‐OX3 (CRY2 overexpressing, line 52.3), and (D) CRY2‐OX8 (CRY2 overexpressing, line 52.8). There was a significant interaction between light treatment and genotype (log‐transformed data; p < 0.001). Different letters above bars indicate significant differences among light treatment × genotype combinations (p = 0.05), thus it allows comparison of bars among figures A–D. Vertical bars indicate SE of the mean of five blocks (n = 5), each based on nine replicate plants

FIGURE 3

Effect of partially (20%) replacing sole red (R), sole blue (B) or red/blue (RB; ratio 3:1) by green (G) light on leaf area on day 21 after transplanting of four tomato genotypes, (A) MM (Moneymaker, wild‐type), (B) cry1a (CRY1a‐deficient), (C) CRY2‐OX3 (CRY2 overexpressing, line 52.3), and (D) CRY2‐OX8 (CRY2 overexpressing, line 52.8). Interaction between light treatment and genotype was significant (log‐transformed data; p < 0.001). Different letters above bars indicate significant differences between light treatments × genotype combinations (p = 0.05), thus it allows comparison of bars among figures A–D. Vertical bars indicate SE of the mean of five blocks (n = 5), each based on three replicate plants

FIGURE 4

Effect of partially (20%) replacing sole red (R), sole blue (B) or red/blue (RB; ratio 3:1) by green (G) light on shoot: Root ratio on day 21 after transplanting of four tomato genotypes, (A) MM (Moneymaker, wild‐type), (B) cry1a (CRY1a‐deficient), (C) CRY2‐OX3 (CRY2 overexpressing, line 52.3), and (D) CRY2‐OX8 (CRY2 overexpressing, line 52.8). A significant interaction between light treatment and genotype was observed (p = 0.013). Different letters above bars indicate significant differences between light treatment × genotype combinations (p = 0.05), thus it allows comparison of bars among figures A–D. vertical bars indicate SE of the mean of five blocks (n = 5), each based on three replicate plants

FIGURE 5

Effect of partially (20%) replacing sole red (R), sole blue (B) or red/blue (RB; ratio 3:1) by green (G) light on total dry weight on day 21 after transplanting of four tomato genotypes, (A) MM (Moneymaker, wild‐type), (B) cry1a (CRY1a‐deficient), (C) CRY2‐OX3 (CRY2 overexpressing, line 52.3), and (D) CRY2‐OX8 (CRY2 overexpressing, line 52.8). No significant interaction between light treatment and genotype was found (p = 0.686), but the effects of light treatment (p = 0.04) and genotype (p < 0.001) were significant. Different letters above bars indicate significant differences between light treatment × genotype combinations (p = 0.05), thus it allows comparison of bars among figures A–D. Vertical bars indicate SE of the mean of five blocks (n = 5), each based on three replicate plants