Radicle growth

Radicle elongation was quite linear with time (r = 0.98, minimum). Pretreating the seed with DCM reduced early radicle growth, but by 96 h the sterol/DCM treated seed achieved radicle lengths equal to that of the H2O control and 30% more than those of DCM controls. The experiment was terminated at 96 h when space limitations in the petri dishes and near-anaerobic conditions during incubation began to interfere with seedling development. There were no secondary roots visible after 96 h. 

J20 stimulated radicle growth of barnyard grass. Cress radicle growth was not stimulated by culture broth of any of the isolates tested. 

Table III. Effect of culture broth (2 ml/petri dish) and dichloromethane extract of culture broth (0.2 mg/petri dish) on cress radicle growth, as related to presence of cyclohex-imide. Data are for all isolates tested in liquid culture whose broth inhibited cress radicle growth to 50% of controls...

Principle Phytotoxic effects of the aqueous leachate of an allelopathic plant can be tested in vitro bioassays. Test or target plants are placed in contact with 0.5 % aqueous leachate from the allelopathic plant. Germination and radicle growth can be monitored during time-course experiments (i.e. after 24,48 and 72 h of treatment), but in this chapter we will include only the results obtained after 72 h of treatment. 

Observations Germination and radicle growth can be determined at 12, 24, 48 and 72 h and the inhibitory effect of the aqueous leachate can be calculated comparing root length of treated seedlings vs. data from control ones. In this case, we only used the 72 h treatment (Figure 1). 

Fig. 1 Effects of aqueous leachate of S. deppei on radicle growth of tomato after 72 h of treatment.

Compounds 58 and 59 showed phytotoxic effects when tested against seedlings of A. hypochondriacus using a Petri dish bioassay. Compounds 58 [IC50 = 6.57 xM] and 59 [IC50 = 3.86 xM] inhibited radicle growth of this species with a similar potency to 2,2—dichlorophenoxyacetic acid [2,4-D IC50 = 18 xM], which was used as a positive control. 

The unharvested parts of rice plants are generally mixed with the soil because this has been thought to be beneficial. It has been observed however, that productivity of the second crop of rice in a paddy is less than that of the first crop. Chou and Lin (45) found that aqueous extracts of decomposing rice residues in soil retarded radicle growth of rice seedlings and growth of rice plants. Maximum toxicity occurred in the first month of decomposition and declined thereafter. Some toxicity persisted for four months in the paddies. Five inhibitory phenolic acids were identified from decaying rice residues and several unidentified allelochemicals were isolated. 

Table I. Effects of the Extracts of Leaves and Roots of Piper aurltum, . hlspldum, Croton pyramldalis, Cecropla obtuslfolla, and Slparuna nlcaraguensls on Radicle Growth of Some Secondary Species...

Reduced germination and inhibition of radicle growth Causes morphological deformities in germinating medic seedlings by interfering with cell division and early growth of meristems... 

Wardle, D. A., Nicholson, K.S., Ahmed, M. Allelopathic influence of nodding thistle (Carduus nutans L.) seeds on germination and radicle growth of pasture plants. New Zealand J Agri Res 1991 34 185-191. 

Certain secondary metabolites are released into the environment and affect the growth and development of different species. The mode/s of action of allelochemicals are diverse, and this knowledge is essential to developmental biology. Previous experiments showed an effect on germination and radicle growth of the hydroxamic acid, 2-benzoxazolinone (BOA), a compound released by plants (mainly grasses) into the environment. Alterations of plant energy metabolism were also reported for BOA. Other effects have been noted, but there are still some doubts about the precise mode of action in the affected plants. 

Once clear inhibitory effects were detected on germination and radicle growth of lettuce plants exposed to BOA,12,35 our group developed methodology to show whether there is a detectable BOA effect on the cell cycle progression in lettuce root meristems.13 This allows a more detailed characterization of the putative direct or indirect effect on the meristems of BOA-treated seedlings. 

A. sedillense aqueous extract only inhibited the radicle growth of bean 25% but tomato radicle growth 60%. In bean root, A. sedillense aqueous extract increased the expression of 16 proteins (Table 14.1, Figs. 14.1A and 14.1B). In treated-tomato roots, 14 proteins were modified. Twelve proteins increased (1-8, 10-11, 13-14), one was detected only in this treatment (9), and another one was repressed (12) (Table 14.1 and Figs. 14.1C and 14.1D). 

Aqueous extract of L. camara inhibited 41% and 81% bean and tomato radicle growth, respectively. However, this treatment modified a similar number of proteins in both plants. In treated-bean roots, the expression of 15 proteins was modified 6 proteins were increased (2, 8-12), and 8 were decreased (3-7 13-15) (Table 14.2, Figs. 14.2A and 14.2B). In tomato treated-roots, 11 proteins were modified six proteins were increased (1-6), and 5 were decreased (7-11) (Table 14.2, Figs. 14.2B and 14.2D). 

---