1 Introduction

Plant hormones have manifold and diverse effects though conditional on plant developmental stage, hormonal concentration as well as site of action (Liu and Chen, 2009; Jaillais and Chory, 2010). They have significant impact on plant growth and development by affecting its cell division, cell differentiation and elongation. These are categorized into five classes, viz., auxins, cytokinins, ethylene, abscisic acid and gibberellins (gibberellic acid). Among these, auxins and gibberellic acid control expansion along longitudinal axes and significantly affect size of organs and plant architecture (Liu and Chen, 2009).Therebyin this research note, differential effect of 6-benzylainopurie (BAP) on potatoes discussed.

2 Plant Material

In vitro micropropagation study was conducted on potato genotype, PRI-red while in vitro regeneration study was based on genotype Kuroda.

2.1 Sprouting and preparation of explant to be used

Tubers of potato (Solanum tuberosum L.) cultivar, PRI-Red were used as source of explant (axillary bud of sprout) in micropropagation. For surface sterilization, tubers were washed with water and dipped in detergent solution containing 2-3 drops of tween-20 for 15 minutes. Thereafter, tubers were rinsed 4-5 times with autoclaved ultra-pure water and soaked in 0.3% GA₃ solution for 15 minutes and 30 minutes. These GA₃ treated tubers were then wrapped with paper bag and kept in dark condition at 26±1˚C for sprouting. After sprouting the tubers, explant was surface sterilized by soaking in ultra-pure water and also in detergent solution containing 2-3 drops of tween-20 for few minutes. After that, sprouted tubers were rinsed 5-6 times with ultra-pure water. Subsequent sterilization operation was done in axenic condition under laminar air flow cabinet. Sprouts were cut into small section containing 1-2 buds each followed by dipping in 70% ethanol for 1 minute and 0.1 HgCl₂ solution for 5 minutes. Thereafter explants were rinsed 4-5 times with ultra-pure water.

2.2 Culture media for in vitro micropropagation

Eight different media were formulated for in vitro micropropagation of cv. PRI-Red. Each medium contains basal MS salt and vitamins, supplemented with 0, 0.75, 1.75, 2.75 mg/l NAA and 0, 0.75, 1.75, 2.75 mg/l BAP, alone or in combination. All media components were mixed together, adjusted to pH 5.7-5.8 and solidified with 2.66 g/l Gellun gum powder. Thereafter, these media were autoclaved at 121˚C and 15 psi for 20 minutes.

2.3 Micropropagated shoots induction

Axillary buds (explant) were cultured on all eight media described, kept at 26±1˚C for 16/8 hrs light/dark regimes and observed daily. After 5d, buds started germination or/shoot induction. Subsequent maintenance of these cultures was achieved by biweekly subcultures.

3 Results and Discussion

When sprouts of 0.3% GA3 treated potato tubers (Figure 1) of cv. PRI-Red were used as explants and were cultured on micropropagation media containing 1.75, 2.75 mg/l BAP, then these so called berries like structures were formed (Figure 2). These berries like structures were of different shapes and sizes (Figure 3). Similarly when calli of cv. Kuroda induced on callus induction medium containing 4.5 mg/l 2-4D were when shifted on regeneration medium containing 4.75 mg/l BAP then same so-called berries like structures were formed (Figure 4). These so-called berries like structure were started sprouting ~2 months after formation. Shoots were started to grow from these so- called berries (Figure 5).

In literature, similar structures were also observed by different scientists but theyall called these, as microtubers. Kanawl et al. (2006) reported on medium containing 0.75 mg/l BAP, Dhaka and Nailwal (2015) reported on medium containing 13.18 μM zeatin, 5.71 μM IAA and 8.49 μM GA₃and Kumar et al. (2014) also reported that and as well as also stated that these microtubers were sprouted. Hence histoanatomy of these so-called berries like structure achieved from my research studies were done. Thus, histoanatomy of these so-called berries like structure and microtubers were performed which revealed that Sclerified layer of cells is visible in epidermal region in both of the case but in berries it is more prominent because the cells are as less elongated and broad as twice as long. An indication of lignin deposition is indicated in the epidermal region, as well as inner cortical region (red coloration) due to Safranin stain, which typically stains secondary wall mainly, composed of lignin and it is totally absent in microtubers where there is the absence of sclerenchyma in inner cortical parenchyma (Figure 6; Figure7). In microtubers, numerous starch granules are also visible in the storage region, which is specific for the tubers (Figure 7). A small constricted area is also indicated in the central portion, which might be due to collapse of delicate parenchymatous cells during growth pressure which is lacking in so called berries (Figure 6). After considering both of the aspects it is inferred that the anatomical structures indicated a clear cut different pattern between microtubers and the so called berries formed. Presence of lignin in berries clearly differentiates them from microtubers because potato tubers do not contain any traces of lignified material. In addition to this berries also do not possess starch granules in their storage tissues which is a characteristic of true potato tubers.

Acknowledgement

We highly acknowledge Director Potato Research Institute Sahiwal, Pakistan for providing us potato germplasm for research works and also acknowledge, Dr. Mansoor Hameed, Associate Professor, Department of Botany; University of Agriculture Faisalabad for providing help in histoanatomy section of this research work.

References

Dhaka M., and Nailwal T.K., 2015, High efficiency macropropagation of potato (Solanum tuberosum L.) cv, Kufri Jyoti in Kumaun Hills, Journal of plant breeding and crop sciences 7(7): 203-210

Jaillais Y., and Chory J., 2010, Unraveling the paradoxes of plant hormone signaling integration, Nat Struct Mol Biol, 17(6): 642–645 

https://doi.org/10.1038/nsmb0610-642

Kanwal A., Amir A., and Kunwar S., 2006, In Vitro Microtuberization of Potato (Solanum tuberosum L.) Cultivar Kuroda-- A New Variety in Pakistan.International Journal of Agriculture &Biology, 1560–8530/2006/08–3–337–340

Kumar V., Deep R., and Madhuparna B., 2014, Callus Induction and Plant Regeneration in Solanum tuberosum L, cultivars (Kufri Chipsona 3 and MP-97/644) via Leaf Explants, International Research Journal of BiologicalSciences 3(6):66-72

Liu Z.H., and Chen W.S., 2009, Role of plant growth regulating substances, Physiology and maintanence, Encyclopedia of life sciences (EOLSS) Vol V