Abstract
Oilseed rape (Brassica napus L.) is a high-boron (B)-demanding crop, and initially, normal growing plants might show B deficiency at advanced growth stages on soils with marginal B availability. Hence, we compared the effects of B resupply via roots and leaves on growth and physiological response, and relative expression of B transporters in B-deficient oilseed rape plants. Four-week-old plants initially grown with inadequate B (1 µM B for the first two weeks and 0.25 µM B for the next two weeks) were later grown either as such with 0.25 µM B, with 25 µM B in nutrient solution or foliar sprayed with 7 mL of 30, 60 and 150 mM B solution plant−1 as boric acid. Plants grown with 25 µM B in the nutrient solution from the beginning were included as adequate B treatment. Results showed that B resupply to B-deficient plants via roots and leaves (60 mM B) equally improved root and shoot dry matter, but not to the level of plants grown with adequate B supply. Foliar-applied 150 mM B proved toxic, causing leaf burn but not affecting dry matter. Resupply of B via roots increased B concentration in roots and leaves, while leaf-applied B did so only in leaves. Net carbon assimilation had a positive relationship with dry matter accumulation. Except for the highest foliar B level, B resupply via roots and leaves increased the accumulation of glucose, fructose and sucrose in leaves. Boron-deficient plants showed significant upregulation of BnaNIP5;1 in leaves and roots and of BnaBOR1;2 in roots. Boron resupply via roots reversed the B-deficiency-induced upregulation of BnaNIP5;1 in roots, whereas the expression of BnaBOR1;2 was reversed by both root and foliar B resupply. In leaves, B resupply by both methods reversed the expression of BnaNIP5;1 to the level of B-adequate plants. It is concluded that B resupply to B-deficient plants via roots and leaves equally but partially corrected B deficiency in B. napus grown in hydroponics.
Highlights
Oilseed rape (Brassica napus L.) is one of the major oilseed crops and used worldwide for animal and human nutrition
We investigated the effect of B resupply via roots and foliage on the growth, B concentration in different tissues, physiological behavior and the relative expression of specific genes involved in B uptake and translocation in B-deficient B. napus plants under hydroponics condition for two weeks
Oilseed rape plants grown under B-deficient conditions showed the symptoms of B deficiency both in the foliar mature leaves and young leaves (Figure 1)
Summary
Oilseed rape (Brassica napus L.) is one of the major oilseed crops and used worldwide for animal and human nutrition. It is highly sensitive to B deficiency, having B requirements higher than 0.5 mg B kg−1 soil [1], and it shows a notable reduction in seed yield and quality under B-deficient conditions [2,3]. Oilseed rape is often cultivated on soils with low or reduced B availability to plants by liming, high soil pH and drought periods during the main growth stages [4,5]. A continuous B supply is important throughout the vegetative and reproductive stages for normal growth of plants. Boron deficiency appears often after hot, dry weather because less B can be absorbed by plants as the top soil dries out. Boron deficiency is considered to inhibit plant growth and reduce yield in oilseed rape [1,6,7]
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