Hanbury Colin D, Atwell Brian J
Department of Agriculture, 3 Baron-Hay Court, South Perth, WA 6151, and Department of Biological Sciences, Macquarie University, Sydney, NSW, Australia.
Ann Bot. 2005 Oct;96(5):913-24. doi: 10.1093/aob/mci243. Epub 2005 Aug 18.
Root axes elongate slowly and swell radially under mechanical impedance. However, temporal and spatial changes to impeded root apices have only been described qualitatively. This paper aims (a) to quantify morphological changes to root apices and (b) assess whether these changes pre-dispose young root tissues to hypoxia.
Lupin (Lupinus angustifolius) seedlings were grown into coarse sand that was pressurized through a diaphragm to generate mechanical impedance on growing root axes. In situ observations yielded growth rates and root response to hypoxia. Roots were then removed to assess morphology, cell lengths and local growth velocities. Oxygen uptake into excised segments was measured.
An applied pressure of 15 kPa slowed root extension by 75% after 10-20 h while the same axes thickened by about 50%. The most terminal 2-3 mm of axes did not respond morphologically to impedance, in spite of the slower flux of cells out of this region. The basal boundary of root extension encroached to within 4 mm of the apex (cf. 10 mm in unimpeded roots), while radial swelling extended 10 mm behind the apex in impeded roots. Oxygen demand by segments of these short, thick, impeded roots was significantly different from segments of unimpeded roots when the zones of elongation in each treatment were compared. Specifically, impeded roots consumed O2 faster and O2 consumption was more likely to be O2-limited over a substantial proportion of the elongation zone, making these roots more susceptible to O2 deficit. Impeded roots used more O2 per unit growth (measured as either unit of elongation or unit of volumetric expansion) than unimpeded roots. Extension of impeded roots in situ was O2-limited at sub-atmospheric O2 levels (21% O2), while unimpeded roots were only limited below 11% O2.
The shift in the zone of extension towards the apex in impeded roots coincided with greater vulnerability to hypoxia even after soil was removed. Roots still encased in impeded soil are likely to suffer from marked O2 deficits.
在机械阻抗作用下，根轴伸长缓慢且径向增粗。然而，关于受阻抗根尖的时空变化仅进行了定性描述。本文旨在：（a）量化根尖的形态变化；（b）评估这些变化是否使幼根组织易受缺氧影响。
羽扇豆（Lupinus angustifolius）幼苗种植于粗砂中，通过隔膜对粗砂施压，从而对生长中的根轴产生机械阻抗。原位观察得出生长速率以及根对缺氧的反应。随后将根取出以评估其形态、细胞长度和局部生长速度。测定了离体根段的氧气吸收情况。
施加15 kPa的压力10 - 20小时后，根伸长速度减缓75%，而相同根轴增粗约50%。尽管细胞从该区域流出的通量较慢，但根轴最末端2 - 3毫米在形态上对阻抗无反应。根伸长的基部边界向根尖内侧缩进至4毫米处（对照：未受阻抗根为10毫米），而在受阻抗根中，径向增粗在根尖后方延伸10毫米。当比较各处理伸长区的情况时，这些短而粗的受阻抗根段的氧气需求与未受阻抗根段显著不同。具体而言，受阻抗根消耗氧气更快，并且在伸长区的很大一部分区域，氧气消耗更可能受限于氧气供应，使得这些根更容易出现氧气亏缺。与未受阻抗根相比，受阻抗根每单位生长（以伸长单位或体积膨胀单位衡量）消耗更多氧气。在低于大气氧气水平（21%氧气）时，原位受阻抗根的伸长受限于氧气供应，而未受阻抗根仅在氧气含量低于11%时才受限于氧气供应。
受阻抗根的伸长区向根尖转移，即使去除土壤后，其对缺氧的脆弱性仍增加。仍包裹在受阻抗土壤中的根可能会遭受明显的氧气亏缺。
