Influence of far-red light coherence on the functional state of plants

The influence of the coherence of far-red (730 nm) light on the functional activity of plants was studied. Blackberry explants cultivated in vitro on an artificial nutrient medium served as a biological model. The explants were irradiated with light beams with different spatial and temporal coherence. The average cell size $D$ was taken as the discrimination threshold for the coherence length $L_{\mathrm{coh}}$ and the correlation radius $r_{\mathrm{cor}}$. The results of irradiation were judged by the length and number of shoots formed on each explant. The greatest photoinduced effect was observed when the conditions $L_{\mathrm{coh}}$, $r_{\mathrm{cor}}>D$ were fulfilled, i.e., when the cell fit completely in the coherence volume of the light wave field. Significant differences in growth parameters were also observed in the variants of the experiment with a constant frequency spectrum of radiation (fixed $L_{\mathrm{coh}}$), but different $r_{\mathrm{cor}}$. It is concluded that the correlation properties of radiation affect photoregulatory processes.

Figure 1

Setup for the experiments with variable coherence. IR filter is infrared filter; R/FR IF is red or far-red interference filter.

Figure 2

Absorption spectra of the Pr and the Pfr form of plant phytochrome (according to [36]), and normalized spectra of the incandescent lamp with filters.

Figure 3

Influence of red or combined (red and 1 min later far-red) light-emitting diode radiation on the length of shoots of blackberry explants. Cultivation period is 30 days.

Figure 4

Dependence of the length of shoots and the multiplication factor of blackberry explants on the time of irradiation with far-red (740 nm) light. Cultivation period is 20 days.

Figure 5

Influence of the coherence of far-red (730 nm) light on the growth indices of blackberry explants. (I) $L_{\mathrm{coh}}=107\mu \mathrm{m}$, $r_{\mathrm{cor}}=18\mu \mathrm{m}$; (II) $L_{\mathrm{coh}}=10\mu \mathrm{m}$, $r_{\mathrm{cor}}=6\mu \mathrm{m}$; (III) $L_{\mathrm{coh}}=11\mu \mathrm{m}$, $r_{\mathrm{cor}}=18\mu \mathrm{m}$; and (IV) $L_{\mathrm{coh}}=11\mu \mathrm{m}$, $r_{\mathrm{cor}}=6\mu \mathrm{m}$. Exposure duration is 480 s, cultivation period is 20 days.

Figure 6

Influence of the duration of irradiation with far-red light with relatively high (variant I) and low (variant IV) coherence on shoots growth inhibition in culture in vitro. Cultivation period is 20 days.

Figure 7

Changes in the length of shoots of blackberry explants after their irradiation with far-red light with relatively high (variant I) and low (variant IV) coherence. Duration of irradiation is 480 s.