Effect of treatments given to the grain, on the growth of wheat roots under drought conditions1

M. S. CARCELLER AND A. SORIANO Departatnet~to de Biologia y Ecologia, Facultad de Agronomia y Veterinaria,

Uiziversidad de Buenos Aires, Buenos Aires, Argentina Received May 17, 1971

CARCELLER, M. S., and A. SORIANO. 1972. Effect of treatments given to the grain, on the growth of wheat roots under drought conditions. Can. J. Bot. 50: 105-108.

The effect of pretreatments given to wheat grains which are supposed to increase drought resistance was studied in young plants under controlled conditions of water stress. In one of the two cultivars used, root growth was found to be significantly greater in plants from pretreated seeds, during and after a period of water stress.

Under conditions of ample water availability, root growth was not influenced by the pretreatments.

CARCELLER, M. S., et A. SORIANO. 1972. Effect of treatments given to the grain, on the growth of wheat roots under drought conditions. Can. J. Bot. 50: 105-108.

Certains pretraiten~ents appliqu6s aux grains de blt sont cens6s augmenter la resistance & la dessi- cation. Les plantules venues de graines ainsi traittes ont kt6 Btudiees sous des conditions contrdldes de deficit en eau. Chez un des deux cultivars etudiks, la croissance des racines a kt6 significativement plus Clevee chez les plantules provenant de graines pretraitkes. Cet effet s'est manifest6 pendant et apr6s la pCriode de deficit en eau.

Quand I'eau ttait abondante, la croissance de la racine n'a pas kt6 influencke par les pretraitements.

Introduction Contradictory results have been obtained by

Certain plants are specially able to survive under drought conditions, either because they can maintain their metabolic activity under low water potential or because they are able to absorb more water and reduce its loss (May and Milthorpe 1962).

Drought resistance is regarded as a property developed during ontogeny, which can thus be increased by special "hardening" treatments (Henckel 1964). According to one of these methods, the seeds are submitted to a period of desiccation after the beginning of imbibition. This treatment should be applied at a state of germination as advanced as it is possible without damaging the embryo. Henckel also states that germination of the seeds in a calcium chloride solution is an effective treatment.

Many authors have reported that higher yields were obtained from a number of crops when the seed had been pretreated, particularly under conditions of water stress but also in full water

other authors when the same general approach was applied to several species. Waisel (1962), Evenari (1964), and Abdel Hafeez and Hudson (1967) found that pretreatments given to the grains failed to increase drought resistance or dry weight production. Differences in the results achieved by these techniques have been generally attributed to variability in response among species or varieties, or to the wide range of experimental conditions used by different authors (Woodruff 1969).

May et al. (1962) have pointed out the need to perform a detailed analysis of the effect of such pretreatments, particularly on the growth during early stages of development, and on the exten- sion of root system and the rate of transpiration in different conditions of soil water potential.

The present experiments describe the effect of pretreatments given to imbibed wheat grains on the subsequent growth of the seedlings kept under controlled conditions of water availability.

availability. Uglov (1964) found increased yields Materials and Methods in wheat together with a extended The wheat cultivars Klein Rendidor and Klein H539 system and reduced water deficits in leaves, bs 1100 were used throughout the experiments. during drought periods. The grains were surface-disinfected with Ca hypo-

chlorite 1% for 20min,rinsed in distilled water 3 times,and lThis work was accomplished during the tenure, by germinated in plastic trays over absorbent paper saturated

the senior author, of a fellowship of the Consejo Nacional with distilled water. They were incubated in darkness at de Investigaciones Cientificas y Tknicas. 20°C.

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106 CANADIAN JOURNAL O f BOTANY. VOL. 50, 1972

The details of the presowing treatments were essentially the same as those described by Waisel (1962). The seeds were weighed and then germinated as indicated above; 18 h later those seeds with emerging radicles were selected and dried over filter paper for 48 h at 25'C. After this period of desiccation, the grains had about recovered their original fresh weight. They were then transferred again to the germination trays.

The pretreatment did not show any effect on germina- tion as growth was normally resumed after the second period of imbibition. The CaC12 pretreatment was given using a 0.25 M solution instead of distilled water. After 24 h of incubation a t 20°C, the germinating grains were selected, rinsed, and transferred to distilled water. The controls were germinated in distilled water and the ger- minating grains were selected 18 h later.

The pretreatments were coordinated so that all the plants were uniform in size when the drought treatments were started (Fie. 1).

After 48 h bf &bation in darkness at 20°C, when the main root had reached 15-25 mm in length, the lateral roots were cut off. The seedlings were transferred to glass tubes, 18 cm long and 3 mm in diameter, lined with absorbent paper. The root was introduced into the tube, while the grain rested in the broadened upper end of the tube (Soriano 1970). At the bottom of the tube, closed by a silicone stopper, a small quantity of water was enough to keep the paper saturated.

The seedlings were grown under continuous fluorescent light in a thermostated bath at 22OC. The roots were also exposed to light.

After a 24-h period, the plants in each treatment were distributed in two lots. They were sorted so that the average lengths of the roots were similar in both lots.

One of the lots in each treatment was then submitted to drought. To achieve this, the water at the bottom of the tube was wiped off and a narrow strip of blotting paper was introduced into the upper end of the tube, leaving a portion of 5 cm emerging from it. This strip acted as a wick speeding up desiccation of the tube lining paper (Soriano 1970). The controls were provided with water whenever necessary, to keep the substrate saturated.

After 48 h of drought the plants were returned to conditions of ample water availability. The wicks were discarded, and the paper lining the tubes was allowed t o rewet slowly from the bottom. In this way the plants were grown for another period of 24 h (period of recovery).

Every 24 h, after the start of the drought treatment, the tubes were placed under a dissecting microscope so that the roots could be measured to the nearest millimeter.

Results

Four experiments were made, all of them showing similar results. The results of one experiment are represented in Fig. 2.

The growth of the roots of control plants under full water availability, was linear throughout the experiment, and closely similar in both cultivars for non-pretreated plants and for both pretreat- ments.

The drought period depressed the root growth, and this effect is shown in Fig. 2. The daily in- crements in both cultivars were reduced to about one-half of that in the control plants.

G E R M I N A T I O N T R A Y S T U B E S

! I / D R O U G H T

I R E C O V E R Y

C 0 E F

Ca C I * a- C 0 E R E C O V E R Y F

24 H O U R S , I

FIG. 1. Timetable for the pretreatments given to the grains. (A) Germinating grains were selected. (B) Lateral roots were cut off and the plants were transferred to tubes. (C) Plants were distributed into two lots and one of them was submitted to water stress. (D, E, F) Root length was measured.

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CARCELLER AND SORIANO: GROWTH OF WHEAT ROOTS 1N DROUGHT 107

Determinations of the water content in the substrate were made at the level where the root tips were growing, and compared to correspond- ing values in the water retention curve for the same material determined in a pressure mem- brane (Richards 1949). A tension greater than 15 atm was noted in this region 48 h after the beginning of drought.

Rewatering did not affect significantly the root growth during the 24-h period of "recovery." Root growth was found to be linear also for droughted plants throughout the experiment.

The pretreatments given to the grain did not affect growth in the plants growing in full water availability, as can be seen in Fig. 2, where root growth increments do not differ significally between non-pretreated seeds and both classes of pretreatments. Under water stress, however, the desiccation pretreatment enhanced the root

C O N 1 ROL

D R O U G H T

growth in plants of Klein H539 bs 1100 cultivar as compared to non-pretreated plants, while in the Klein Rendidor cultivar root growth was depressed by the same pretreatment.

Root growth of desiccation-pretreated plants in Klein H539 bs 1100, after 24 h of drought was 73y0 of that of the same plants growing with an ample water supply. After 48 h this value was 59y0 with respect to the same control. These values were significantly higher than those for non-pretreated plants, and were consistently found in all experiments.

The CaC12-pretreated plants in both cultivars behaved like non-pretreated plants.

Discussion The roots of desiccation-pretreated plants of

cultivar Klein H539 bs 1100 showed a significant difference in growth during the drought period,

CONTROL

OROUGHT

POOLED 1 STAN;;;;R

H O U R S

FIG. 2. Accumulated daily increment of wheat roots growth. Mean values of eight roots per treatment. In droughted plants, root length was measured 24 and 48 h after beginning of water stress, and 24 h after rewatering. Control roots were measured at the same time. Initial root length: Klein Rendidor, non-pre- treated 58 mm, desiccation 57 mm, CaClz 41 mm; Klein H539 bs 1100, non-pretreated and desiccation 59 mm, CaClz 54 mni. Desiccation as pretreatment - - -, CaC12 as pretreatment - - -, non-pretreated ----.

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108 CANADIAN JOURNAL OF BOTANY. VOL. 50. 1972

as compared to non-pretreated plants. The possibility of ascribing differences in response to age differences was minimized by the experi- mental schedule already described. The seeds were selected so that when the desiccation pre- treatment was applied they were all in the same stage of germination. The CaClz and the non- pretreated seeds were equally selected; the seeds of delayed germination were discarded. Drought tolerance may vary with age, but the lots of seedlings submitted to water stress were of the same size for all treatments.

Depending on the cultivar used, presowing treatments can be effective or not in increasing drought tolerance, or can even decrease it. This has already been suggested in many papers. Michajlikov and Juarez (1953) found that pre- treating wheat and maize grains improves yield, especially during years of pronounced drought, but the effect was more remarkable in some varieties.

The results obtained also indicate that the difference in root growth is only brought about under conditions of water stress. Whenever water was fully available, root growth was similar in pretreated and non-pretreated plants.

According to Henckel (1964) changes in the protoplasmic properties were responsible for difference in behavior of pretreated plants. This author found an increase in viscosity and elasticity and a greater water retention capacity, as a result of increase in hydrophyllic colloids. As a consequence, metabolic processes were stimulated and their rate was maintained at a higher level during water stress.

May et al. (1962), analyzing the results ob- tained by Henckel, concluded that the claimed increase in yield of hardened plants is variable under drought conditions, and is hardly present at all when water is fully available. Increased resistance to drought of pretreated plants could be explained by the possession of a larger root system, and changes in protoplasmic structure would be the consequence of water stress. On the other hand, Woodruff (1969) found a higher relative water content in leaves of wheat plants from treated seeds, grown under conditions

where an increased root area does not appear to cause the phenomenon.

The roots of pretreated plants of cultivar Klein H539 bs 1100 are able to withstand extreme conditions of water stress and to keep, in such conditions, a higher growth rate than the un- treated ones. As the roots of untreated plants can also grow considerably under conditions of drastic water stress, the difference resulting from the pretreatment might be only quantitative.

However, under drought conditions, an in- creased root growth rate may represent an appreciable advantage to pretreated plants. This is in coincidence with the conclusions from May et al. (1962) that increased drought resistance in pretreated plants is only a result of increased absorption of water by a larger root system.

Acknowledgments The authors gratefully acknowledge the help of

Mr. Daniel Ginzo with statistical analysis of data.

ABDEL HAFEEZ, A. T., and J. P. HUDSON. 1967. Effect of "hardening" radish seeds. Nature (London), 216: 688.

EVENARI, M. 1964. Hardening treatment of seeds as a means of increasing yield under conditions of in- adequate moisture. Nature (London), 204: 101Ck1011.

HENCKEL, P. A. 1964. Physiology of plants under drought. Annu. Rev. Plant Physiol. 15: 363-386.

MAY, L. H., and F. L. MILTHORPE. 1962. Drought re- sistance of crop plants. Field Crop Abstr. 15: 171-179.

MAY, L. H., E. J. MILTHORPE, and F. L. MILTHORPE. 1962. Presowing hardening of plants to drought. An appraisal of the contributions of P. A. Henckel. Field Crou Abstr. 15: 93-98.

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RICHARDS, L. A. 1949. Methods of measuring soil moisture tension. Soil Sci. 68: 95-112.

SORIANO, A. 1970. Crecimiento y relaciones con el agua, de la planta joven de trigo sometida a condiciones de sequia. Rev. Fac. Agron. Vet. Buenos Aires, 18(1): 51-58.

UGLOV, P. D. 1964. Effect of presowing hardening of summer wheat seeds on drought resistance under con- ditions of the Tselinny region. Sov. Plant Physiol. 10: 399401.

WAISEL, Y. 1962. Pre-sowing treatments and their re- lation to growth and to drought, frost and heat resist- ance. Physiol. Plant. 15: 4346.

WOODRUFF, D. R. 1969. Studies on presowing drought hardening of wheat. Aust. J. Agric. Res. 20: 13-24.

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