Acid Phosphatase Activity in Phosphorus-Deficient White Lupin Roots - Assignment Example

Word count 1610 A critical review on Gilbert, GA, Knight, JD, Vance, CP & Allan, DL 1999, ‘Acid phosphatase activity in phosphorus-deficient white lupin roots’, Plant, Cell and Environment, vol. 22, pp. 801-810. SUMMARY: In this research communication the authors have observed the course of phosphate hydrolyzing enzymes under phosphorus stressed conditions. White lupins produce proteoid or cluster roots also along with normal roots. Under phosphorus starvation these cluster roots show vigorous branching. Plants were cultivated in sand culture and proteins from root exudates and extracts had been isolated and assayed by methods already standardised. The data were obtained by more than one method and results of the experiments are presented by graphs and gels and also analysed by ANOVA. The major findings of the research are: four fold increase in acid phosphatase from phosphorus deficient (–P) proteoid root exudates compared to Phosphorus sufficient (+P) normal roots and two fold more than the –P normal roots (p803). Molybdate enhanced proliferation of proteoid roots in plants receiving organic phosphates (glycerophosphate or phytate) as source of phosphorus. The -P conditions induced a new isoform (isoform 2) of acid phosphatase which moved faster on gel. This –P induced isoform 2 along with isoform 1 was found both in the exudates and extracts of –P normal roots also, though the quantity was much higher in the proteoid roots. The isoform 2 appeared at 12 DAE (days after emergence) in –P plant root. Phytase activity decreased in both types of roots under P deficiency compared to the plants grown in P sufficient conditions. The study had been conducted with the aim to characterise acid phosphatase and phytase activities in the root exudates and extracts of white lupin plants. Authors have monitored the degree, location and timing of activities of these enzymes. Through this research they have elucidated the role of phosphatases in lupin nutrition and their course during P deficiency. The research question may be posed as: Does phosphorus deficiency influence time, degree and location of acid phosphatase and phytase activities in lupin roots? Phosphorus availability is independent variable while the timing, extent and location of acid phosphatase and phytase activities and root types are dependent variables in this experiment. The experimental procedures have given description of tests conducted while tables, graphs and electrophoresis photographs presented results sequentially. Researchers have broadly stated the hypothesis, in a general manner. The reader is not able to find the specific aspect of their research viz. the adaptive response of plant roots by producing a different isoform of acid phosphatase in huge quantities to overcome phosphorus limitation and also the inhibitory effects of the competitive inhibitor used in the study. The background of research is presented in the introduction. It gives brief discussion about white lupin root morphology under phosphorus starvation, types of phosphates available in soils and ability of the plants to utilise these. The literature referred also provides characteristics of acid phosphatases and location and action of plant phytases.The importance of induced isoforms of acid phosphatase, as adaptive responses under P limitation, is however not emphasised well though it is one of the major research and discussion aspect of the paper. The role of phytase is stated to be unclear in the introduction. Authors have used the word suspected as: The role of extracellular acid phosphatases is generally suspected to be the mobilization of organic P from soils for plant nutrition (p. 802). I feel that using ‘assume’ or ‘seem’ appropriately would have given positive meaning. Introduction has adequately emphasised importance of organic phosphates present in soil as major forms of phosphorus i.e. up to 30-80%. Hence the role of lupin roots to mobilise it through citrate exudation as one strategy that holds great relevance to cultivating crops in phosphorus limited soils. The introduction is kept basic just as the hypothesis being tested and the title of the paper is also simple. The purpose of study, to provide strategies of plant to overcome nutrient limitation, is rather lightly touched. The introduction has repeatedly, and also the abstract, emphasised proteoid or cluster roots as adaptation to phosphorus deficiency giving impression that these roots are exclusively present in phosphorus starved plants. However it is reported, at p803, that “up to 10% of root dry weight can be proteoid even in P-sufficient roots (Johnson et al. 1994)”, thus proteoid root formation is not an adaptation to phosphorus starved condition while extensive proliferation of these roots certainly is. Does methodology provide sufficient details for repeating the experiments? The experiment was a completely randomised design with phosphorus treatment and root types as the factors (803). The planting conditions are explained in adequate details and could be repeated by other workers. They had rightly chosen molybdate which is potent inhibitor and to a great extent specific to acid phosphatases. The researchers have given sufficient description for isolation of proteins from root extract and exudates. They have used standard procedures for enzyme assays, gel electrophoresis and in vivo enzyme detection. These procedures are verified and recommended by the manufacturers of the equipments used in this study. The results are authentic since four replicates of each experiment are tested and the outcomes verified with more than one procedure. The alternative explanations are provided wherever discrepancy have aroused. So within the limits of errors applicable to biological material the procedures can be replicated by other workers. It may be assumed that even if other workers do not get the same values, they would certainly get the same trend. There, however, are a few minor points which may confuse some workers. These are: planting the seeds is not clearly indicated e. g. how many seeds for each experiment and in how much sand? Did they use sterilised sand? Besides, phytase activity assays were conducted at 55 °C instead of 20 °C or 37 °C. The researchers had chosen high reaction temperature to reduce incubation time, which was otherwise up to 24 h at lower temperatures. However, it would not reflect the actual level of activity of these enzymes in root environment. They have overlooked considering it as unimportant adaptive response and only a minor enzyme though certainly influenced by phosphorus limitation. Similarly while detecting in vivo phosphatase the agarose was allowed to set at room temperature and then placed in a refrigerator for up to 24 h to visualise dark purple colour of enzyme activity which again is rather lower temperature than actual root temperature. The researchers have not communicated about temperature ranges for activity of these enzymes to convince the reader. These are some minor point which most scientists may not at all consider as deterrent in repeating the experiments or modify easily to their own logic. The results are presented clearly in graphs, tables and photographs to support the narration. However the ANOVA tables should have captions with details of data. For e. g. there are stars on some data but these are not explained in table legends. As a results reader has to read and reread the text again and again in an attempt to associate text with the tables. Otherwise also, as biologists we are somewhat scared of statistics and mathematics and hence do not retain these for long. Some of the results needed more clarification. For example, The conclusion that isoform 2 is specifically abundant in proteoid roots is not supported by fig 4 on p 806 where the normal root exudates of -P has only isoform 2 and no isoform 1 of acid phosphatase. It can not be ignored merely as discrepancy in protein loading on the gel since the result has clarity. The alternative explanation could be that normal roots are major producers of acid phosphatases (including the isoform2). The enzymes are then passed on to proteoid roots as these can utilise the enzymes more efficiently on account of greater surface area and probably higher uptake ability (permeability) for phosphorus from rhizosphere released after enzyme activity. Such a hypothesis could be future research option as well. Despite these discrepancies the results do support the hypothesis. The degree, timing and location of enzyme induction in two types of roots are throughout measured as was the aim. Probably it is a preliminary research on the aspect hence the authors have proceeded with a simple title and hypothesis though they have provided sufficient scope for further characterisation of the enzymes. As a major outcome, the study has provided a logical explanation that proteoid roots are major sites of production and/ or activity of more useful isoform 2 under P limitation. Induction of isoform 2 occurs along with production of isoform1 of acid phosphatase under-P conditions. Unlike normally present isoform 1, this enzyme is not inhibited by molybdate but is similar in action to isoform 1 as it also helps in mobilising phosphorus from organic sources. Huge amounts of isoform 2 in association with extensive proliferation of cluster roots in –P or glycerophosphate+ molybdate plants are clearly an adaptive strategy of white lupin to overcome P starvation. The additional finding has been that molybdate inhibits acid phosphatases hydrolysing organic phosphorus sources. Could they have given more information for future research? Authors have provided alternative explanations for increased phosphatase activity up to 16 DAE and production of somewhat lesser amounts of isoform 2 under the effect of molybdate in –P plant. The authors could have given alternative explanation in light of their findings. Such as, there was increase in acid phosphatase and induction of new isoform (isoform 2) of this enzyme but at the same time decrease in the phytase activity in –P plants. Why does the exudates from normal roots of –P show only isoform 2 as in fig 4?. These findings too could have been explained in same manner for providing future research scopes. The results also encourage future researchers to look in to the aspects of identification and availability of inducer for isoform 2 production. Read More