I think theres a point in thinking about how does a plant/leaf come to be erect. Afai understand there has to be some water travelling thru the plant for this to happen, water attracts water which leads to a column of water to rise thru the plant. Sort of like an inflating bounce castle. Once this already happening the plant can go into that weird all leaves vertical praying when the plant limits exposure to light for the top. Not happening in nature? Well natural light is not like articial: it is fairly constant in that unshaded leaves 1m down gets the same amount of light as top. But in a grow room this is not quite the same: unshaded leaves 2m from the light gets considerably less light than top leaves due to intensity falling off. So its not strange if this is an indoor phenomena.
Everything mentioned by peeps above on why can be related to the pillar of water rising thru the plant: its capacity to draw water and its need to draw water. Roots must be there and the solution mustn't be so strong that it draws water out of the roots. Environment must be right for the plant to want to shed some heat by transpiring. It needs enough light by the right quality (mainly blue but some red) for the stomata to open wide.
Some foliars as stephen mentioned. CO2: with high levels they close stomata cause theyre allready getting enough. So you basicly need the input and the output of water in the plant to be on point for this to happen.
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@SDS_GR in reference to blue/green light reactions do you know if the stomata aperture is a part of blue light reaction in the sense that it is reversed by green light? In the sense that if i wanted to increase stomata apeture but without the rest of blue light reactions would giving green light at the same time let the stomata open but compensate the extra blue light? Youre usually the man for these things
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