Enhancement of chilling resistance of inoculated grapevine plantlets with a plant growth-promoting rhizobacterium, Burkholderia phytofirmans strain PsJN

Abstract

In vitro inoculation of Vitis vinifera L. cv. Chardonnay explants with a plant growth-promoting rhizobacterium, Burkholderia phytofirmans strain PsJN, increased grapevine growth and physiological activity at a low temperature. There was a relationship between endophytic bacterial colonization of the grapevine plantlets and their growth at both ambient (26 degrees C) and low (4 degrees C) temperatures and their sensitivities to chilling. The major benefits of bacterization were observed on root growth (11.8- and 10.7-fold increases at 26 degrees C and 4 degrees C, respectively) and plantlet biomass (6- and 2.2-fold increases at 26 degrees C and 4 degrees C, respectively). The inoculation with PsJN also significantly improved plantlet cold tolerance compared to that of the nonbacterized control. In nonchilled plantlets, bacterization enhanced CO(2) fixation and O(2) evolution 1.3 and 2.2 times, respectively. The nonbacterized controls were more sensitive to exposure to low temperatures than were the bacterized plantlets, as indicated by several measured parameters. Moreover, relative to the noninoculated controls, bacterized plantlets had significantly increased levels of starch, proline, and phenolics. These increases correlated with the enhancement of cold tolerance of the grapevine plantlets. In summary, B. phytofirmans strain PsJN inoculation stimulates grapevine growth and improves its ability to withstand cold stress.

FIG. 1.

Effect of chilling injury on the weight of grapevine plantlets. (A) Nonchilled plantlets. (B) Chilled plantlets. Error bars indicate standard deviations.

FIG. 2.

Light micrographs of grapevine leaves. Twelve-week-old plantlets were subjected to 4°C treatment during 2 weeks, whereas the control remained at 26°C. (a) Control plantlets. (b) Bacterized plantlets. (c) Control plantlets chilled at 4°C. (d) Bacterized plantlets chilled at 4°C. No obvious correlation between cold treatment and marked host wall alterations or heavy tissue damages was observed. For both bacterized plantlets grown at 26°C and bacterized chilled plantlets, the cross-section showed an accumulation of starch grains in leaf parenchyma as indicated by the arrows. Ep, epidermis; P, parenchyma; S, starch. Magnification for panels a, b, and d, ×20; magnification for panel c, ×40.

FIG. 3.

Light micrographs of grapevine shoots. Twelve-week-old plantlets were subjected to 4°C treatment during two weeks, whereas the control remained at 26°C. (a) Control plantlets. (b) Bacterized plantlets. (c) Control plantlets chilled at 4°C. (d) Bacterized plantlets chilled at 4°C. For both bacterized plantlets grown at 26°C and bacterized chilled plantlets, a cross-section showed an accumulation of starch grains in shoot stele as indicated by the arrows. Bacterized plantlet shoots indicate the presence of secondary structure as evidenced by a net development of xylem (black arrowheads). No obvious correlation between cold treatment and marked host wall alterations or heavy tissue damage was observed. Ep, epidermis; Co, cortex; P, pith; Vs, vascular stele. Magnification, ×40.

FIG. 4.

Light micrographs of grapevine roots. Twelve-week-old plantlets were subjected to 4°C treatment during 2 weeks, whereas the control remained at 26°C. (a) Control plantlets. (b) Bacterized plantlets. (c) Control plantlets chilled at 4°C. (d) Bacterized plantlets chilled at 4°C. Roots of chilled plantlets showed obvious correlations between cold treatment and marked host wall alterations and tissue damage in the epidermis (Ep) and the cortex (Co), as indicated by the arrows. Magnification, ×40.