Adventitious Roots Of Rice Research Articles

Adventitious roots in rice, the model cereal: genetic factors and the influence of environmental cues—a mini review

Adventitious roots in rice, the model cereal: genetic factors and the influence of environmental cues—a mini review

Longitudinal Pattern of Aerenchyma Formation Using the Ti-Gompertz Model in Rice Adventitious Roots.

The longitudinal pattern of root aerenchyma formation of its relationship with the function of adventitious roots in rice remains unclear. In this study, the percentage of the aerenchyma area to the cross-sectional area (i.e., aerenchyma percentage) was fit with four non-linear models, namely, W0-Gompertz, Ti-Gompertz, logistic, and von Bertalanffy. Goodness-of-fit criteria such as the R2, the Akaike information criterion (AIC), and the Bayesian information criterion (BIC) were used to select the model. The bias of the parameters was evaluated using the difference between the ordinary least squares-based parameter estimates and the mean of 1,000 bootstrap-based parameter estimates and the symmetry of the distributions of these parameters. The results showed that the Ti-Gompertz model, which had a high goodness-of-fit with an R2 close to 1, lower AIC and BIC values, parameter estimates close to being unbiased, and good linear approximation, provided the best fit for the longitude pattern of rice aerenchyma formation with different root lengths among the competing models. Using the second- and third-order derivatives according to the distance from the root apex, the critical points of Ti-Gompertz were calculated. The rapid stage for aerenchyma formation was from the maximum acceleration point (1.38–1.76 cm from the root apex) to the maximum deceleration point (3.13–4.19 cm from the root apex). In this stage, the aerenchyma percentage increased by 5.3–15.7% per cm, suggesting that the cortical cells tended to die rapidly for the aerenchyma formation rather than for the respiration cost during this stage. Meanwhile, the volume of the aerenchyma of the entire roots could be computed using the integral function of the Ti-Gompertz model. We proposed that the longitudinal pattern of root aerenchyma formation modeled by the Ti-Gompertz model helped to deeply understand the relationship between the anatomical traits and physiological function in rice adventitious roots.

Abscisic acid is required for exodermal suberization to form a barrier to radial oxygen loss in the adventitious roots of rice (Oryza sativa).

To acclimate to waterlogged conditions, wetland plants form a barrier to radial oxygen loss (ROL) that can enhance oxygen transport to the root apex. We hypothesized that one or more hormones are involved in the induction of the barrier and searched for such hormones in rice. We previously identified 98 genes that were tissue-specifically upregulated during ROL barrier formation in rice. The RiceXPro database showed that most of these genes were highly enhanced by exogenous abscisic acid (ABA). We then examined the effect of ABA on ROL barrier formation by using an ABA biosynthesis inhibitor (fluridone, FLU), by applying exogenous ABA and by examining a mutant with a defective ABA biosynthesis gene (osaba1). FLU suppressed barrier formation in a stagnant solution that mimics waterlogged soil. Under aerobic conditions, rice does not naturally form a barrier, but 24 h of ABA treatment induced barrier formation. osaba1 did not form a barrier under stagnant conditions, but the application of ABA rescued the barrier. In parallel with ROL barrier formation, suberin lamellae formed in the exodermis. These findings strongly suggest that ABA is an inducer of suberin lamellae formation in the exodermis, resulting in an ROL barrier formation in rice.

Silicon induces adventitious root formation in rice under arsenate stress with involvement of nitric oxide and indole-3-acetic acid.

Arsenic (As) negatively affects plant development. This study evaluates how the application of silicon (Si) can favor the formation of adventitious roots in rice under arsenate stress (AsV) as a mechanism to mitigate its negative effects. The simultaneous application of AsV and Si up-regulated the expression of genes involved in nitric oxide (NO) metabolism, cell cycle progression, auxin (IAA, indole-3-acetic acid) biosynthesis and transport, and Si uptake which accompanied adventitious root formation. Furthermore, Si triggered the expression and activity of enzymes involved in ascorbate recycling. Treatment with L-NAME (NG-nitro L-arginine methyl ester), an inhibitor of NO generation, significantly suppressed adventitious root formation, even in the presence of Si; however, supplying NO in the growth media rescued its effects. Our data suggest that both NO and IAA are essential for Si-mediated adventitious root formation under AsV stress. Interestingly, TIBA (2,3,5-triiodobenzoic acid), a polar auxin transport inhibitor, suppressed adventitious root formation even in the presence of Si and SNP (sodium nitroprusside, an NO donor), suggesting that Si is involved in a mechanism whereby a cellular signal is triggered and that first requires NO formation, followed by IAA biosynthesis.

Oxygen in the air and oxygen dissolved in the floodwater both sustain growth of aquatic adventitious roots in rice.

Flooding is an environmental stress that leads to a shortage of O2 that can be detrimental for plants. When flooded, deepwater rice grow floating adventitious roots to replace the dysfunctional soil-borne root system, but the features that ensure O2 supply and hence growth of aquatic roots have not been explored. We investigate the sources of O2 in aquatic adventitious roots and relate aerenchyma and barriers for gas diffusion to local O2 gradients, as measured by microsensor technology, to link O2 distribution in distinct root zones to their anatomical features. The mature root part receives O2 exclusively from the stem. It has aerenchyma that, together with suberin and lignin depositions at the water-root and cortex-stele interfaces, provides a path for longitudinal O2 movement toward the tip. The root tip has no diffusion barriers and receives O2 from the stem and floodwater, resulting in improved aeration of the root tip over mature tissues. Local formation of aerenchyma and diffusion barriers in the mature root channel O2 towards the tip which also obtains O2 from the floodwater. These features explain aeration of floating roots and their ability to grow under water.

Root aeration in rice (Oryza sativa): evaluation of oxygen, carbon dioxide, and ethylene as possible regulators of root acclimatizations

Adventitious roots of rice (Oryza sativa) acclimatize to root-zone O(2) deficiency by increasing porosity, and induction of a barrier to radial O(2) loss (ROL) in basal zones, to enhance longitudinal O(2) diffusion towards the root tip. Changes in root-zone gas composition that might induce these acclimatizations, namely low O(2), elevated ethylene, ethylene-low O(2) interactions, and high CO(2), were evaluated in hydroponic experiments. Neither low O(2) (0 or 0.028 mol m(-3) O(2)), ethylene (0.2 or 2.0 microl l(-1)), or combinations of these treatments, induced the barrier to ROL. This lack of induction of the barrier to ROL was despite a positive response of aerenchyma formation to low O(2) and elevated ethylene. Carbon dioxide at 10 kPa had no effect on root porosity, the barrier to ROL, or on growth. Our findings that ethylene does not induce the barrier to ROL in roots of rice, even though it can enhance aerenchyma formation, shows that these two acclimatizations for improved root aeration are differentially regulated.

FPF1 transgene leads to altered flowering time and root development in rice

AtFPF1 (FLOWERING PROMOTING FACTOR 1) is a gene that promotes flowering in Arabidopsis. An expression vector containing AtFPF1 driven by a Ubi-1 promoter was constructed. The gene was introduced into rice callus by Agrobacterium-mediated transformation and fertile plants were obtained. The presence of AtFPF1 in rice plants was confirmed by PCR, Southern and Northern blot analyses, as well as by beta-glucuronidase assay. The results showed that, as in Arabidopsis, AtFPF1 reduced flowering time in rice. Furthermore, introduction of AtFPF1 enhanced adventitious root formation but inhibited root growth in rice during the seedling stage. The results suggest that AtFPF1 promotes flowering time in both dicots and monocots, and plays a role in the initiation of adventitious roots in rice.

A comparison of NH4+ and NO3– net fluxes along roots of rice and maize

Net fluxes of NH4+ and NO3– along adventitious roots of rice (Oryza sativa L.) and the primary seminal root of maize (Zea mays L.) were investigated under nonperturbing conditions using ion‐selective microelectrodes. The roots of rice contained a layer of sclerenchymatous fibres on the external side of the cortex, whereas this structure was absent in maize. Net uptake of NH4+ was faster than that of NO3– at 1 mm behind the apex of both rice and maize roots when these ions were supplied together, each at 0·1 mol m–3. In rice, NH4+ net uptake declined in the more basal regions, whereas NO3– net uptake increased to a maximum at 21 mm behind the apex and then it also declined. Similar patterns of net uptake were observed when NH4+ or NO3– was the sole nitrogen source, although the rates of NO3– net uptake were faster in the absence of NH4+. In contrast to rice, rates of NH4+ and NO3– net uptake in the more basal regions of maize roots were similar to those near the root apex. Hence, the layer of sclerenchymatous fibres may have limited ion absorption in the older regions of rice roots.

Evidence for the involvement of ethene in aerenchyma formation in adventitious roots of rice (Oryza sativa L.)

summaryTwo varieties of rice (ev. Norin 36 and RB3) were either grown in stagnant or aerated 1/4‐strength Hoagland's solution with or without exogenous ethene and a range of silver concentrations (an ethene antagonist), or were grown in flooded and drained soils.With cultivar Norin 36, AgNO3 was very effective in reducing porosity by inhibiting aerenchyma development. This effect was antagonized by gassing with increasing concentrations (1 or 2 μ1−l) of ethene. The results are consistent, therefore, with reports that cavity formation in roots is controlled by endogenous levels of ethene. Also, porosity varied with root length, and if a correction was made for this, the inhibitory effect of the silver ion on aerenchyma development appeared to be even greater.For the cultivar RB3, root porosities in solution culture appeared initially to be unaffected by ethene or AgNO2, but root lengths were reduced and root numbers increased by increasing ethene concentration. When these effects on root length were taken into account, it was concluded that ethene had increased root porosity, and AgNO3, had decreased it. Consistent with earlier studies, and with the ethene hypothesis, aerenchyma development in both varieties was also enhanced by soil waterlogging, with percentage porosities 12 units higher in flooded than in drained soil. The porosities of cv, RB3 were higher than those for cv. Norin 36, however, and the regression line of porosity against root length was steeper, indicating a greater predisposition to form aerenchyma in cv. RB3. This was confirmed in solution‐grown roots, where AgNO3 had no significant effect on porosity in stagnant or in aerated roots of cv. RB3, and both 1 and 2 μ1−1 ethene increased the porosity in cv. RB3 roots to a similar level. Silver nitrate, however, did antagonize the effects of 1 and 2 μ1−1 ethene. In contrast, porosity in cv. Norin 36 was progressively reduced by AgNO3.It is concluded that, although there are intervarietal differences in sensitivity, an ethene promotion of gas‐space formation can occur in rice, and ethene should not be ruled out as the endogenous promoter.

A Transmission and Cryo-Scanning Electron Microscopy Study of the Formation of Aerenchyma (Cortical Gas-Filled Space) in Adventitious Roots of Rice (Oryza sativa)

Webb, J. and Jackson, M. B. 1986. A transmission and cryo-scanning electron microscopy study of the formation of aerenchyma (cortical gas-filled space) in adventitious roots of rice (Oryza sativa).— J. exp. Bot. 37: 832-841. The initiation and development of aerenchyma in adventitious roots of rice (Oryza sativa) was studied in tissue up to approximately 36-h-old using transmission electron microscopy (TEM) and cryo scanning electron microscopy (cryo-SEM). Aerenchyma resulting from selective cortical cell collapse is a naturally occurring feature of rice roots. Evidence of some cortical cell disruption was noticeable by TEM in cells that were approximately 6-h-old; it became more advanced as the cells aged. At 12 h, early stages of cell wall breakdown and loss of cell turgidity were seen. Complete collapse of columns of cells had occurred by 24 h. In tissue that was 36-h-old, the senescent cytoplasm of many remaining cells began to disperse. The visual evidence suggests that cell collapse was the result of autolysis. This pattern of cortical degeneration in rice was dissimilar to that reported elsewhere for Zea roots grown in an oxygen depleted environment. Cryo-SEM revealed the occurrence of small structures within the cortex with the external appearance of miniature, intact cells which are not preserved during conventional SEM preparative procedures.

Aerenchyma (Gas-space) Formation in Adventitious Roots of Rice (Oryza sativaL.) is not Controlled by Ethylene or Small Partial Pressures of Oxygen

Jackson, M. B., Fenning, T. M., and Jenkins, W. 1985. Aerenchyma (gas-space) formation in adventitious roots of rice (Oryza sativa L.) is not controlled by ethylene or small partial pressures of oxygen.—J. exp. Bot. 36: 1566-1572. The extent of gas-filled voids (aerenchyma) within the cortex of adventitious roots of vegetative rice plants (Oryza sativa L. cv. RB3) was estimated microscopically from transverse sections with the aid of a computer-linked digitizer drawing board. Gas-space was detectable in 1-d-old tissue and increased in extent with age. After 7 d, approximately 70% of the cortex had degenerated to form aerenchyma. The extent of the voids in 1-4-d-old tissue was not increased by stagnant, poorly-aerated external environments characterized by sub-ambient oxygen partial pressures and accumulations of carbon dioxide and ethylene. Treatment with small oxygen partial pressures, or with carbon dioxide or ethylene applied in vigorously stirred nutrient solution also failed to promote the formation of cortical gas-space. Furthermore, ethylene production by rice roots was slowed by small oxygen partial pressures typical of stagnant conditions. Silver nitrate, an inhibitor of ethylene action, did not retard gas-space formation; similarly when endogenous ethylene production was inhibited by the application of aminoethoxyvinylglycine (AVG), aerenchyma development continued unabated. Cobalt chloride, another presumed inhibitor of ethylene biosynthesis, did not impair formation of the gas in rice roots nor did it decrease the extent of aerenchyma even if AVG was supplied simultaneously. These results contrast with those obtained earlier using roots of Zea mays L. We conclude that in rice, aerenchyma forms speedily even in well-aerated environments as an integral part of ordinary root development. There seems to be little or no requirement for ethylene as a stimulus in stagnant root-environments where aerenchyma is likely to increase the probability of survival.