A natural plant growth promoter calliterpenone from a plant Callicarpa macrophylla Vahl improves the plant growth promoting effects of plant growth promoting rhizobacteria (PGPRs)

Experiments were conducted to evaluate the efficacy of calliterpenone, a natural plant growth promoter from a shrub Callicarpa macrophylla Vahl., in enhancing the growth and yield promoting effects of plant growth promoting rhizobacteria (PGPRs), in menthol mint (Mentha arvensis L).This study is based on our previous results indicating the microbial growth promotion by calliterpenone and assumption that application of calliterpenone along with PGPRs will improve the population of PGPRs resulting in higher impacts on plant growth and yield. Of the 15 PGPRs (identified as potent ones in our laboratory), 25 μl of 0.01 mM calliterpenone (8.0 μg/100 ml) was found to be useful in improving the population of nine PGPRs in culture media. The five selected strains of PGPRs exhibiting synergy with calliterpenone in enhancing growth of maize compared to PGPR or calliterpenone alone were selected and tested on two cultivars (cvs. Kosi and Kushal) of M. arvensis. Of the five strains, Bacillus subtilis P-20 (16S rDNA sequence homologous to Accession No NR027552) and B. subtilis Daz-26 (16SrDNA sequence homologuos to Accession No GU998816) were found to be highly effective in improving the herb and essential oil yield in the cultivars Kushal and Kosi respectively when co-treated with calliterpenone. The results open up the possibilities of using a natural growth promoter along with PGPRs as a bio-agri input for sustainable and organic agriculture.     

Biomechanics of plant growth

Growth of turgid cells, defined as an irreversible increase in cell volume and surface area, can be regarded as a physical process governed by the mechanical properties of the cell wall and the osmotic properties of the protoplast. Irreversible cell expansion is produced by creating a driving force for water uptake by decreasing the turgor through stress relaxation in the cell wall. This mechano-hydraulic process thus depends on and can be controlled by the mechanical properties of the wall, which in turn are subject to modification by wall loosening and wall stiffening reactions. The biochemical mechanisms of these changes in mechanical wall properties and their regulation by internal signals (e.g., hormones) or external signals (e.g., light, drought stress) are at present incompletely understood and subject to intensive research. These signals act on walls that have the properties of composite materials in which the molecular structure and spatial organization of polymers rather than the distribution of mechanical stresses dictate the allometry of cell and organ growth and thus cell and organ shape. The significance of cell wall architecture for allometric growth can be demonstrated by disturbing the oriented deposition of wall polymers with microtubule-interfering drugs such as colchicine. Elongating organs (e.g., cylindrical stems or coleoptiles) composed of different tissues with different mechanical properties exhibit longitudinal tissue tensions resulting in the transfer of wall stress from inner to peripheral cell layers that adopt control over organ growth. For physically analyzing the growth process leading to seed germination, the same mechanical and hydraulic parameters as in normal growth are principally appropriate. However, for covering the influences of the tissues that restrain embryo expansion (seed coat, endosperm), an additional force and a water permeability term must be considered.     

Ascorbate and plant cell growth

Ascorbate and related enzymes are involved in the control of several plant growth processes. Ascorbate modulates cell growth by controlling (i) the biosynthesis of hydroxyproline-rich proteins required for the progression of G1 and G2 phases of the cell cycle, (ii) the cross-linking of cell wall glycoproteins and other polymers, and (iii) redox reactions at the plasma membrane involved in elongation mechanisms. The effect of ascorbate on onion root elongation is reviewed here. The ascorbate free radical induces a high vacuolization responsible for elongation. This effect may be dependent on the activity of the redox system linked to the plasma membrane. Current data are discussed on the basis of the modulation of the plasma membrane energetic state derived from the ascorbate-induced hyperpolarization and the activity of an intrinsic transplasmalemma ascorbate-regenerating enzyme.     

Chemical control of plant growth

The latest applications of physiologic principles to the solution of agricultural and horticultural problems involve the use of synthetic hormones to stimulate rooting of cuttings, to effect blossom thinning in fruit production, to prevent pre-harvest fruit drop, to produce seedless fruit, to achieve control of weeds, to break as well as to prolong dormancy, and to bring about other economically important controls of plant growth.     

Inositol signaling and plant growth

Living organisms have evolved to contain a wide variety of receptors and signaling pathways that are essential for their survival in a changing environment. Of these, the phosphoinositide pathway is one of the best conserved. The ability of the phosphoinositides to permeate both hydrophobic and hydrophilic environments, and their diverse functions within cells have contributed to their persistence in nature. In eukaryotes, phosphoinositides are essential metabolites as well as labile messengers that regulate cellular physiology while traveling within and between cells. The stereospecificity of the six hydroxyls on the inositol ring provides the basis for the functional diversity of the phosphorylated isomers that, in turn, generate a selective means of intracellular and intercellular communication for coordinating cell growth. Although such complexity presents a difficult challenge for bench scientists, it is ideal for the regulation of cellular functions in living organisms.     

Diurnal regulation of plant growth

Life occurs in an ever-changing environment. Some of the most striking and predictable changes are the daily rhythms of light and temperature. To cope with these rhythmic changes, plants use an endogenous circadian clock to adjust their growth and physiology to anticipate daily environmental changes. Most studies of circadian functions in plants have been performed under continuous conditions. However, in the natural environment, diurnal outputs result from complex interactions of endogenous circadian rhythms and external cues. Accumulated studies using the hypocotyl as a model for plant growth have shown that both light signalling and circadian clock mutants have growth defects, suggesting strong interactions between hypocotyl elongation, light signalling and the circadian clock. Here, we review evidence suggesting that light, plant hormones and the circadian clock all interact to control diurnal patterns of plant growth.     

Kinematics of plant growth.

Many of the concepts and equations which have been used in the study of compressible fluids can be applied to problems of plant development. Growth field variables, i.e. functions of position in the plant and of time, can be specified in either Eulerian (spatial) or Lagrangian (material) terms. The two specifications coincide only when the spatial distribution of the variable is steady, and steady patterns are most likely to emerge when an apex is chosen as origin of the co-ordinate system. The growth field itself can be described locally by the magnitude and orientation of the principal axes of the rate of strain tensor and by the vorticity tensor. Material derivatives can be calculated if the temporal and spatial variation in both growth velocity, u (rate of displacement from a material origin), and the variable of interest are known. The equation of continuity shows the importance of including both growth velocity, u, and growth rate, ▽ ·u in estimates of local biosynthesis and transport rates in expanding tissue, although the classical continuity equation must be modified to accommodate the compartmentalized distributions characteristic of plant tissue. Relatively little information on spatial variation in plant organs can be found in the botanical literature, but the current availability of interactive computer graphics equipment suggests that analysis of the spatial distribution of growth rates at least is no longer difficult.     

Allometric relations in plant growth

Allometric relations Y = aX^b are shown to exist in phyllotaxis, under the form r = k log R = p ()(m + n) ^–2 , where r = Y is the normalized internode distance in the cylindrical representation of phyllotaxis and R is the plastochrone ratio in the centric representation, p()=a is a constant for every angle of intersection of the opposed parastichies of the visible pair (m, n), for every m and n, and for all possible limit divergence angles corresponding to the Fibonacci-type sequences..., m–n, n, m, m + n=X, 2m + n, ..., and where b=–2. Richards' phyllotaxis index will be deduced.This work was supported by the Natural Science and Engineering research Council Canada, grant A6240     

Oligopeptides as plant growth regulators

It is generally accepted that plant growth and development are regulated by the known plant hormones. Some objections to the functions of auxins and cytokinins in the induction of shoot and root primordia are reported. Instead of them oligopeptides of special amino acid sequences could be the endogenous signals. There exist structure relationships between auxins and parts of the α-helical oligopeptides of defined amino acid sequences. The same is true for cytokinins. The most difficult part of this hypothesis is its verification. Using protonemata ofFunaria hygrometrica bud induction by various oligopeptides was investigated. The most active peptide tested is leucine-tryptophan. On the other hand endogenous oligopeptides containing [¹⁴C]-leucine in the moss protonemata during endogenous bud initiation were looked for. Three to four different oligopeptide spots seem to be related to bud induction.     

Heterogeneous growth of plant tissues

KORN, R., 1993. Heterogeneous growth of plant tissues. Heterogeneous growth is defined as different rates or patterns of growth in adjacent tissue regions, in contrast to homogeneous growth where a region expresses a uniform rate or pattern of growth. Heterogeneous growth is inspected in a variety of plant tissues and the pattern of expansion is characterized for each. In the case of epidermal cell proliferation, different growth rates for cell plates and old walls lead to the feature of coordinated growth in which slow growth of the former is compensated for by a faster rate of the latter. Examples include leaf epidermal cells above veins growing differently from those above areole regions, and pairs of guard cells of stomata ceasing to expand before other epidermal cells. In the alga Coleochaete only marginal walls grow, and at different rates around the colony, to generate a fractal, stochastic type of coordinated growth. In the fern gametophyte there are complex gradients of differential growth rates. Epidermal cells of apices are often of mixed growth, as cells at the summit undergo two dimensional expansion while cells along the flanks express one dimensional expansion. Coordinated growth requires matched rates where the constraining effect of the slower growing region is compensated for by a faster rate in an encircling region compared to the average rate of the overall tissue. Mixed and differential growth patterns do not necessarily create constraints and so lead to smooth tissue expansion. Emergence of some constraints leads to breaking of symmetry and disruptive growth as in the appearance of new axes found in organs and epidermal derivatives. In planar development heterogeneous growth appears to be the rule, and homogeneous growth the exception.     

Quinones as plant growth regulators

The effects of benzoquinone, naphthaquinone and anthraquinone on the growth of tomato callus, whole plants of tomato and on rooting of mungbean cuttings were studied. Naphthaquinone effects on some oxidases and on the isozyme patterns of peroxidases in all the three systems were also observed. Quinones increased callus growth, the number of roots initiated in mungbean cuttings and the growth of tomato plants, significant increases being obtained with 10^–5 M naphthaquinone. Naththaquinone also decreased the activities of IAA oxidase, ascorbic acid oxidase and polyphenol oxidase, and led to the disappearance of one of the isozyme of peroxidase in all systems.     

Modeling plant growth and development

Computational plant models or 'virtual plants' are increasingly seen as a useful tool for comprehending complex relationships between gene function, plant physiology, plant development, and the resulting plant form. The theory of L-systems, which was introduced by Lindemayer in 1968, has led to a well-established methodology for simulating the branching architecture of plants. Many current architectural models provide insights into the mechanisms of plant development by incorporating physiological processes, such as the transport and allocation of carbon. Other models aim at elucidating the geometry of plant organs, including flower petals and apical meristems, and are beginning to address the relationship between patterns of gene expression and the resulting plant form.