CHANGES IN LEAF WATER STATUS IN GRAPEVINE GRAFTINGS TREATED WITH GROWTH REGULATORS

The effect of foliar application of plant growth regulators, paclobutrazol (1000 mg/L), chlorcholine chloride (200 mg/L) and gibberellic acid (100 mg/L) on leaf water status in grapevine graftlings of cv Cardinal was investigated. After stratification and waxing, young vines were planted into vegetation pots and grown in a glasshouse. Foliar treatments were applied once, twice or three times during the vegetative period, starting on 25 July and every 15 days thereafter. Values of total water potential (ΨL) and of relative water content (RWC) were measured over the same period. Results indicate a tendency of increased ΨL values in leaves of plants repeatedly treated with a growth inhibitor paclobutrazol (-1.18 Mpa) compared with untreated (-1.36 Mpa) as well as plants treated twice with gibberellic acid (-1.37 Mpa). RWC in leaves was significantly increased in the second half of the vegetative period when paclobutrazol was applied twice (78%) in comparison with control (75%). Values of both investigated indices point to a more favourable water status of plants treated during the vegetative period with growth inhibitors compared with untreated and plants treated with gibberellic acid.


I n t r o d u c t i o n
The use of the growth inhibitors resulted in the achievement of significant results in regulating the process of growth and maturation of different fruit species.
The primary effects of their application on plants reflect in the inhibited prolongation of young shoots, i.e. reduced growth which is the result of gibberellic acid biosynthesis inhibition.The degree of growth reduction depends on the concentration, time and method of the use of inhibitors.Secondary effects of their application reflect in the changes of photosynthetic activity, chlorophyll content (D a v i s et al.  1985).The plant water regime determines the direction and intensity of a series of physiological processes, on which the quantity and quality of grown plants yield depends.The research was conducted on grapevine graftings in the periods of formation of root system and development of young shoots, when the plant water status is of great significance for rhyzogenic processes and vegetative development of grapevine graftings.

Material and Methods
These studies were conducted in a controlled environment (vegetative pots).Graftings of cv Cardinal onto rootstock Kober 5BB were used as experimental material.
The following growth regulators were used in this trial: 1. Paclobutrazol, at a concentration 1000 mg/L 2. Chlorcholinchloride, at a concentration 200 mg/L 3. Gibberellic acid, at a concentration 100 mg/L Depending on the treatment, regulators were applied to graftings once, twice or three times during the vegetative period, starting on 25 June at 15-day intervals.The treatments applied were as follows: 1. Paclobutrazol applied once (PC1), twice (PC2), or three times (PC3) 2. Chlorcholinchloride applied once (CC1), twice (CC2), or three times (CC3) 3. Gibberellic acid applied once (GA1), twice (GA2), or three times (GA3) 4. Control (C), untreated plants Applications of GA as well as pure water served as untreated reference for observing the effect of treatments using the above growth inhibitors.
Leaf area was measured with the method of "round slices" (J e l e n i c and D ž a m i c , 1989).Total water potential in leaf was determinated with "pleasure chamber" (S h o l a n d e r et al. 1965).Relative water content (RWC) in the leaf was determined with gravimetrical method (S l a t y e r and B a r r s , 1965).Measures were conducted in the period of August, September and October.

Average leaf area
The use of paclobutrazol and chlorcholinchloride caused the reduction of leaf area in the treated grapevine graftings.The reduction of leaf area in the CC2 treatments was statistically very significant and in the CC3 and PC2 treatments significant, (Table 1).With similar concentrations of paclobutrazol T u k e y , 1986; I n t r i e r i , 1986; S a n s a v i n i et al., 1986, also state significant reduction of leaf area.C o o m b e , (1967) reports the occurrence of smaller, thicker and darker leaves after the chlorcholinchloride treatment in comparison with the untreated ones.Gibberelic acid treatments exhibited opposite effects on the leaf area.In GA2 treatment the increase of leaf area was statistically significant compored with the control.The values obtained by measuring Ψ L in August, September and October did not differ significantly among the tested treatments, (Table 2).A mild tendency of total water potential increase in the leaves of multiple treated growth retardants was noticable.If we observe average values of total water potential for the tested period, higher Ψ L values in the plants with multiple paclobutrazol (-1,22 MPa; -1,18 MPa) and chlorcholinchloride (-

Relative water content (RWC)
The results of measuring RWC conducted in August showed that the used growth retardants did not cause significant changes in RWC in comparison with untreated plants.Measuring conducted in September showed that RWC value was much greater in the PC2 treatment comparedwith the untreated plants, (Table 3).In October in the leaves from PC2, PC3, CC2, CC3 treatments RWC values were significantly higher than the untreated plants.F l e t c h e r and N a t h (1984) also state that the plants treated with growth retardants have higher water content in leaves in comparison with untreated plants, more rational water consumption and that they are more tolerant to drought.Paclobutrazol applied once (PC1), twice (PC2), or three times (PC3) Chlorcholinchloride applied once (CC1), twice (CC2), or three times (CC3) Gibberellic acid applied once (GA1), twice (GA2), or three times (GA3) Control (C), untreated plants Since the more favourable water regime was stated in the treatments in which a significant inhibition of leaf areas was realized as well, more efficient water consumption could be related to the reduction of transpiration area.Some researches also point to some significant changes of ABA status and transpiration reduction in the plants treated with preparations from the triasole group, which also includes paclobutrazol (A s a r e -B o a m a h et al. 1986).

C o n c l u s i o n
Multiple foliar application of paclobutrazol (1000 mg/L) and chlorcholinchloride (200 mg/L) lead to the reduction of leaf area of the treated plants.In the same treatments, changes of leaf water potential were also established: Ψ L was slightly increased compared with untreated plants, and RWC values in the leaves of treated plants were significantly higher in comparison with untreated plants, (Figure 1).GA treatments showed opposite effects on the tested indices from the applied growth retardants.The exhibited plant reaction can be significant in stressful situations -drought, as well as in the conditions of poor supply of plants with water.
1988), respiration, carbohydrate content (S t e f f e n s et al. 1983; W a n g et al. 1986) and stress tolerance (S t e f f e n s et al. 1983; S w i e t l i k and M i l l e r , 1983; L o r e n z i and G i u l i v o ,

Fig. 1 .
Fig. 1. -Changes in leaf area, relative water content and total water potential of cv.Cardinal / Kober 5BB graftings as function of application of growth regulators, paclobutrazol (PC), chlorholine chloride (CC) and gibberellic acid (GA) 1,22 MPa; -1,23 MPa) treatments were clearly noticable.So far, research results show that after the use of paclobutrasole water potential of the treated plants was increased (A t k i n s o n and C r i p s , 1983; S w i e t l i k and Miller, 1983).