Low root zone temperature favours shoot B partitioning into young leaves of oilseed rape (Brassica napus)

Abstract

In previous studies with tropical plant species, low root zone temperature (RZT) induced boron (B) deficiency, but it is not known if the same response to RZT will be expressed in temperate species, like oilseed rape, that are more tolerant of low temperature. The present experiments investigated the effect of RZT (10 and 20°C) on oilseed rape (Brassica napus L. cv. Hyola 42) response to B in solution culture, in summer and winter. Regardless of canopy growth conditions, low RZT (10°C) promoted the partitioning of shoot B to the actively growing leaves, especially when B supply was low. However, low RZT did not significantly alter net B uptake rates or plant biomass. Low RZT decreased the shoot‐to‐root ratio, countering the effects of low B which increased it, leading to a decreased demand for B in the shoot at low RZT. At low B supply, B‐deficiency symptoms appeared later at 10 than at 20°C, corresponding with higher B concentrations in the youngest fully opened leaves (YOLs) at 10°C RZT. Thus 10°C RZT increased the tolerance to low B supply. As a result, it is concluded that the effect of decreasing RZT on the responses of the temperate species, oilseed rape, to low B supply depends on whether the low RZT is above or below the optimal root temperature for growth.

Boron Nutrition and Chilling Tolerance of Warm Climate Crop Species

“…Because in most crop species, B is passively taken up by roots, transported in the xylem and deposited towards sinks with the highest transpiration rate (Brown and Shelp, 1997;Hu and Brown, 1997), chilling effects on root water absorption and hydraulic conductance in roots and shoots may suppress root B uptake and transport, and alter B partitioning into new shoot growth (as observed by Ye et al, 2000Ye et al, , 2003. Molecular approaches may be applied to reveal primary events involved in the complex interaction between chilling temperature and B deficiency on the activity and abundance of water channels, root hydraulic conductance and B absorption.…”

“…In chilling-sensitive species like cassava, sunflower and tomato, root chilling-induced reduction of B absorption rate and enhanced B deficiency (Table 1) are likely to be caused by decreased root hydraulic conductance and water absorption, apart from the direct effect of chilling on root absorption surface area and the root : shoot ratio. However, at similar root zone temperature (10-15 C), chillingtolerant species, such as oilseed rape, are capable of maintaining high root hydraulic conductance and root growth (Aroca et al, 2001), which may explain why root chills did not decrease the net B uptake rate in oilseed rape plants at 10 C in the root zone, compared with 20 C (Ye et al, 2003).…”

“…Forno et al, 1979;Macduff et al, 1987;Ye et al, 2000Ye et al, , 2003. The intrinsic chilling sensitivity of crop species seems to be a determining factor in responses of B uptake/transport and B partitioning to root chills (Table 1).…”

“…In a less chilling-sensitive species, tomato (Lycopersicon esculentum 'Burpee') (Kratsch and Wise, 2000), reduction in B uptake at 93 mM B only occurred after root temperature was decreased to 10 C (Tindall et al, 1990). However, exposure to 10 C in the root zone did not decrease B uptake in chilling-tolerant species, such as oilseed rape and wheat (Huang et al, 1996;Ye et al, 2003), because this temperature is above their chilling threshold (Macduff et al, 1987). In the chilling-tolerant winter crop oilseed rape, root growth is tolerant to low root temperature, leading to an increased root : shoot ratio at 10 C in the root zone temperature (Kacperska and Szaniawski, 1993).…”

“…at 0Á25 mM B in sunflower at 12 C) (Forno et al, 1979;Tindall et al, 1990;Ye et al, 2000). In contrast, low root temperature (10 C) delayed B deficiency in chilling-tolerant species like oilseed rape compared with 20 C in the root zone (Ye et al, 2003), through maintaining root growth and B uptake rate and increasing B partitioning into new shoot growth. The difference in leaf stomatal control between chilling-sensitive species and tolerant species at marginal temperatures such as 10 C may explain their different responses in chilling-induced B deficiency sensitivity at about the same root temperature (10-12 C), though 10 C was above the threshold temperature for oilseed rape roots.…”