Regulation of Tuber Formation in the Potato Plant

100

Using high pressure liquid chromatography, the cucumber cotyledon bioassay, and mass spectrometry a cytokinin isolated from Solaum tuberoswn L. cv. Katahdin plant tissues has been identified as cis-zeatin riboside. Zeatin riboside (ZR) levels in plants grown under inducing conditions (28 C day and 13 C night with a 10-hour photoperiod) were significantly higher than those in plants grown under noninducing conditions (30 C day and 28 C night with an 18-hour photoperiod). The highest level of ZR was noted in below-ground tissue after 4 days exposure to inducing conditions, with tuber initiation observed after 8 days. A companion study conducted to determine the effect of ZR on in vitro tuberization of noninduced rhizomes revealed that after 1 month in culture, controls exhibited 0% tuberization, while ZR treatments of 0.3 and 3.0 milligrams per liter showed 39 and 75% tuberization, respectively.The tuberization process in the potato (Solanum tuberosum L.) is thought to be controlled by environmental factors, mainly photoperiod and temperature, which regulate levels ofendogenous growth substances. Short days and cool night temperatures (inducing conditions) have been reported to favor tuberization while long days and high night temperatures delay or inhibit the process (9,13,28).Several workers (7,8,21) have suggested the existence of a tuber-forming stimulus which is formed in leaves under inducing conditions and translocated to below-ground tuberization sites.Other workers have demonstrated the movement of a tuber-forming stimulus from an induced scion through a graft union to below-ground rhizomes which subsequently tuberized (17,25).Although the exact nature of this tuber-forming stimulus remains unknown, it has been speculated that it may be similar to cytokinins (6). Similarly, Palmer and Smith (26) have demonstrated the requirement for cytokinins for in vitro tuberization of excised rhizomes. Results of this laboratory (11,12,18) have supported the theory that the tuberizing factor may be cytokininlike in nature, in that total cytokinin activity was significantly higher in induced than noninduced plants. Two 'To whom reprint requests should be sent.In an attempt to elucidate the structure of potato cytokinins, Anstis and Northcote (1) reported isolating a compound which co-chromatographed with ZR.5 Recently, Van Staden (31) found an N-6-substituted adenyl compound in potato tissue using MS. Accordingly, the objectives of the present study were 2-fold: first, to attempt to isolate and identify the major cytokinin in Katahdin potato tissues; and second, to measure levels of this cytokinin in the plant in an effort to ascertain its possible role in the tuberization process.MATERIALS AND METHODS Plant Tissue. Plant material used in this study was obtained by planting tubers of S. tuberosum L. cv. Katahdin in flats of moist Perlite. Tubers were incubated in a growth chamber adjusted to 28 C day and 25 C night with a 16-hr photoperiod. Growth chambers provided a light intensity of 660 ft-c at pot level. ...

Section: Discussionsupporting

confidence: 83%

“…Other workers have demonstrated the movement of a tuber-forming stimulus from an induced scion through a graft union to below-ground rhizomes which subsequently tuberized (17,25).…”

Section: Introductionmentioning

confidence: 99%

Physiology of Tuberization in Solanum tuberosum L

Mauk

Langille²

1978

100

“…The role ofplant hormones in the tuberization process has been studied to evaluate the nature ofthe tuberization stimulus. Tuberization of the stolons is promoted by cytokinins (7,8,14) and inhibited by GA3 (7,12,22). Although ABA has been shown to promote tuberization in Solanum andigena (22), it inhibited cytokinin-mediated tuberization of Solanum tuberosum (7).…”

Section: Introductionmentioning

confidence: 99%

Effect of Calcium on Tuberization in Potato (Solanum tuberosum L.)

Balamani¹,

Veluthambi²,

Poovaiah³

1986

Tuberization response of single-node leaf cuttings from induced potato plants (Solanum tuberosum L.) was reversed when pretreated with 5 millimolar ethyleneglycol-bis4(i-aminoethyl ether)N,N'-tetraacetic acid (EGTA) + 50 micromolar calcium ionophore (A23187) and resumed when transferred to a CaC12-containing medium. Tuberization was inhibited by LaCI3, chlorpromazine, and trifluoperazine at 5 to 10 micromolar. These results suggest a role for calcium in the tuberization process.Tuberization in potato plants is controlled by environmental and nutritional factors which are known to affect the levels of endogenous growth substances (9, 22). Short days and cool night temperatures promote tuberization whereas long days, high night temperatures, and high nitrogen fertilization delay or inhibit the process (6,10,17). The role ofplant hormones in the tuberization process has been studied to evaluate the nature ofthe tuberization stimulus. Tuberization of the stolons is promoted by cytokinins (7,8,14) and inhibited by GA3 (7,12,22). Although ABA has been shown to promote tuberization in Solanum andigena (22), it inhibited cytokinin-mediated tuberization of Solanum tuberosum (7). Ethylene inhibited tuberization (11) and the role of auxin in this process has not been studied in detail (9).In this study, we have investigated the possible role of Ca in mediating the tuberization stimulus using single-node leaf cuttings from induced potato plants (3,4,13 (2,13). Under the experimental conditions described here, tuberization of the axillary buds of leaf cuttings could be readily observed in 5 to 7 d (Fig. 1). As attempted earlier in carrot suspension cultures (5), 5 mm EGTA (pH adjusted to 7) and the Ca ionophore A23 187 were used together to deplete intracellular and extracellular Ca. In the cuttings pretreated with water or 5 mM EGTA, the axillary buds formed tubers after their subsequent transfer either to water or to 1 mM CaCl2 + 1 mM MgCl2 (Fig. 1B). After pretreatment with 5 mM EGTA + 50 tLM A23187 and subsequent transfer to water the axillary buds of the leaf cuttings did not develop into tubers (Fig. IC)

“…However, tubers do not always develop even from underground buds of cuttings. As with whole plants, tuberization of cuttings is apparently controlled by an unknown "tuberization stimulus" (5,10,19 MATERIALS AND METHODS Clones. Potato ( Solanum tuberosum L., Group Andigena) clones used in this study were obtained through the Cornell University program to select from an Andigena population lines that have Tuberosum-like characteristics (6).…”

mentioning

confidence: 99%

Shoot, Stolon, and Tuber Formation on Potato (Solanum tuberosum L.) Cuttings in Response to Photoperiod

Ewing¹,

Wareing²

1978

115

The intensity of "tuberization stimulus" in potato shoots (Solanum tuberosum L.) can be assessed from cuttings containing one or more leaves. Cuttings maintained in a mist chamber under long days wil form tubers from underground buds If prior to taking the cutting the leaves received sufficient exposure to photoperiods less than the critical photoperiod. The greatest tendency to tuberize was found in cuttings that consisted of a single, fully expanded leaf and its subtended bud. Grafts showed that genetical differences in critical photoperiod resided in properties of the leaf. Short days before cutking tended to shift growth from above ground buds of two-node cuttings to below ground buds, even if the number of short days was insufficient for tuber induction. As few as 6 short days reduced growth of shoots at the upper bud and increased underground growth of shoots and stolons.however, and this trait can be accentuated by breeding (9, 21). In addition to short days, the tuberization stimulus is favored by cool temperatures (3, 11,22,24), by low rather than high rates of N fertilization (24), and by "physiologically old" mother tubers (15,18).Grafting experiments (5, 10), especially the demonstration that even a small piece of stem from an induced plant is capable of transmitting the tuberization stimulus (14), suggest that the stimulus is hormonal in nature. The exact identity of the hormone(s), although extensively investigated, has yet to be established.In this paper we report on the relationships between the exposure of potato foliage to particular photoperiods, the genetically determined CPP, and the levels of tuberization stimulus as reflected by tuberization of cuttings. We show that the CPP characteristic of a given clone is a function of properties of the leaf, not of the underground growing point; and we present evidence that short days shift growth from above ground to below ground buds, even if the number of short days is insufficient for tuber induction. Although potato tubers ordinarily form on underground stolons, every axillary bud on a potato stem has the potential to develop a tuber. Nearly a century ago, Vochting (23) demonstrated that sessile tubers developed at the covered nodes when cut pieces of stem were inserted into soil. He also showed that tuber formation was promoted by darkness and moisture. Recent evidence (16,17) suggests that elevated CO2 levels may also favor tuberization at below ground rather than above ground buds. However, tubers do not always develop even from underground buds of cuttings. As with whole plants, tuberization of cuttings is apparently controlled by an unknown "tuberization stimulus" (5,10,19 MATERIALS AND METHODS Clones. Potato ( Solanum tuberosum L., Group Andigena) clones used in this study were obtained through the Cornell University program to select from an Andigena population lines that have Tuberosum-like characteristics (6). Andigena accessions were screened to obtain three clones with CPP of approximately 12 to 13 hr. Populations of "Neo-Tuber...