The adaxial (upper) surface of the leaf consists of an epidermal layer, cuticle and densely packed layer of palisade mesophyll cells, meant for optimize light capture. The abaxial (lower) surface of the leaf consists of an epidermis with abundant stomata and spongy mesophyll cells for gaseous exchange and regulation of transpiration. The leaf vasculature is-xylem tissue differentiating adaxially and the phloem abaxially.

Thus, the leaf morphology and anatomy play important role in growth response in vitro. Possible reasons are:

1. Upper surface more smooth and has more surface area for nutrient absorption than lower surface as stated by Dr. Karpova

2. In tissue culture, explant vasculature, viz., xylem tissues are more responsive, and xylem tissue differentiate adaxially, thus better option for positive response.

Hello!

This position allows to obtain the greatest amount of nutrients from the medium due to the maximum area of contact between the leave and the surface of the medium. So, regeneration proceeds more efficiently.

The adaxial (upper) surface of the leaf consists of an epidermal layer, cuticle and densely packed layer of palisade mesophyll cells, meant for optimize light capture. The abaxial (lower) surface of the leaf consists of an epidermis with abundant stomata and spongy mesophyll cells for gaseous exchange and regulation of transpiration. The leaf vasculature is-xylem tissue differentiating adaxially and the phloem abaxially.

Thus, the leaf morphology and anatomy play important role in growth response in vitro. Possible reasons are:

1. Upper surface more smooth and has more surface area for nutrient absorption than lower surface as stated by Dr. Karpova

2. In tissue culture, explant vasculature, viz., xylem tissues are more responsive, and xylem tissue differentiate adaxially, thus better option for positive response.

Dear @Oxana Karpova, @Hiranjit Choudhury & @Stefano D'Alessandro

Thank you very much for the kindly answers

Dear Shiva,

I want to complement the answers of Oxana and Hiranjit, and others, from a physiological approach. Remember that on the leaf there is a physiological gradient of growth regulators or hormones and other important metabolites such as calcium. When changing the position it is altered, and consequently the in vitro response changes. For physical and physiological reasons, the piece of leaf you have put in your culture medium, it takes more time to react, and perhaps develop callus, an unwanted response.

Dear Shiva and other! I've a different view and observation, especially when you're working with Agrobacterium mediated transformation of leaves/cotyledons. Putting the adaxial (upper) surface down during co-cultivation and for the 1st 15 days is nice. However, after that the proximal ends of cotyledons/leaves could bend upward due to may be the auxin accumulation at the point of contact with the medium. Then the proximal end may not be in good contact with the medium and turning the explants other ways might improve regeneration of transgenic plants. This could also again depend on the type(variety/explant) we use. We've got different results and people may consider this option.

Used it for different plants. It always works. And one is getting little shoots without them developing thru callus. Its nice to ask why. As some explain that there is better connection with the medium underneath and direct and more efficient use of the hormones in order to regenerate shoots instead of callus.

Thus: why is the tendency of plant samples to convert into callus? Answer with a question

Answer with a very pertinent and till-date not fully resolved question Dr. Wenkart !! As you are aware, considerable research has been going on in this area to answer why? Thanks Dr Wenkart for the question.

Plant cells/ tissue develop unorganized cell masses like callus in response to various biotic and abiotic stimuli like wounding, plant hormones etc. Molecular basis of callus formation though not fully understood, but research in this field is finally allowing scientists to understand how unscheduled cell proliferation is suppressed during normal plant development and how genetic and environmental cues override these repressions to induce callus formation. It is so far learnt from recent studies that many of these naturally occurring calli are formed through the modulation of plant hormone signaling, in particular, of auxin and cytokinin. Several key regulators of these hormone signaling pathways {e.g., ARFs (Auxin Response Factors) and ARRs (Arabidopsis Response Regulators)} function during callus induction. More research is needed to decode how they promote the reacquisition of cell proliferative competence. It is also becoming clear that the formation of some calli uses intrinsic developmental programs, such as embryogenesis and meristem formation. These programs are spatially and temporally restricted under normal growth conditions but appear to get ectopically activated after experiencing certain environmental challenges. It is likely that these hormonal and developmental pathways are interconnected at multiple levels, and further examination of these highly intersecting molecular networks offers one of the major challenges in future studies (from Ikeuchi et al. 2013).

Please go through the link:

Article Plant Callus: Mechanisms of Induction and Repression

Thanks for the long and elaborated answer.

In addition to what Dr Oxana said, the area possess active cells which led to rapid regeneration.

While, to what Dr. Beleke mentioned; in Agro-transformation OR even shoot regeneration the adaxial part is recommended to put onto the media to allow new plantlet initiation/induction/regeneration etc. Thanks ALL

hello

thank you all

To obtain a greater amount of nutrition from the feeder circles. Therefore, growth continues to be more efficient.

regards