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Time course and auxin sensitivity of cortical microtubule reorientation in maize roots
E B Blancaflor1, K H Hasenstein
1Department of Biology, University of Southwestern Louisiana, Lafayette 70504-2451, USA.
Abstract:
The kinetics of MT [microtubule] reorientation in primary roots of Zea mays cv. Merit, were examined 15, 30, 45, and 60 min after horizontal positioning. Confocal microscopy of longitudinal tissue sections showed no change in MT orientation 15 and 30 min after horizontal placement. However, after 45 and 60 min, MTs of the outer 4-5 cortical cell layers along the lower side were reoriented. In order to test whether MT reorientation during graviresponse is caused by an auxin gradient, we examined the organization of MTs in roots that were incubated for 1 h in solutions containing 10(-9) to 10(-6) M IAA. IAA treatment at 10(-8) M or less showed no major or consistent changes but 10(-7) M IAA resulted in MT reorientation in the cortex. The auxin effect does not appear to be acid-induced since benzoic acid (10(-5) M) did not cause MT reorientation. The region closest to the maturation zone was most sensitive to IAA. The data indicate that early stages of gravity induced curvature occur in the absence of MT reorientation but sustained curvature leads to reoriented MTs in the outer cortex. Growth inhibition along the lower side of graviresponding roots appears to result from asymmetric distribution of auxin following gravistimulation.
Insights
Microtubule reorientation in corn roots occurs after 45 minutes of horizontal placement, suggesting a role for auxin gradients in gravity response. Sustained curvature leads to microtubule changes in the outer cortex.
Area of Science:
- Plant biology
- Cell biology
- Gravitropism
Background:
- Microtubules (MTs) play crucial roles in plant cell structure and response to stimuli.
- Gravitropism, the growth of plants in response to gravity, involves complex cellular signaling pathways.
Purpose of the Study:
- To investigate the timing and mechanism of microtubule reorientation in Zea mays (corn) roots during gravitropism.
- To determine if auxin gradients are responsible for MT reorientation in response to gravity.
Main Methods:
- Confocal microscopy was used to observe microtubule organization in longitudinal sections of corn roots.
- Roots were subjected to horizontal positioning for varying durations (15-60 minutes).
- Roots were treated with different concentrations of Indole-3-acetic acid (IAA) to assess auxin's effect on MTs.
Main Results:
- Microtubule reorientation was observed in the outer cortical cells of corn roots 45-60 minutes after horizontal placement.
- Treatment with 10(-7) M IAA induced MT reorientation, suggesting a role for auxin.
- The region near the maturation zone was most sensitive to IAA, and auxin's effect was not acid-induced.
Conclusions:
- Early stages of gravity-induced root curvature occur without MT reorientation.
- Sustained gravitational stimulus leads to MT reorientation in the outer cortex.
- Asymmetric auxin distribution following gravistimulation likely causes growth inhibition on the lower side of the root.