O rebento murchou com o calor.

Here rebento means a shoot, sprout, or new plant growth.

In European Portuguese, it can refer to:

• a young shoot from a plant
• a new bud or sprout
• sometimes, in other contexts, a child/offspring in a figurative or informal way

In this sentence, because of murchou and calor, it clearly refers to a plant shoot.

O is the definite article: the.
Um would mean a/an.

So:

• O rebento murchou = The shoot wilted
• Um rebento murchou = A shoot wilted

Portuguese often uses the definite article in places where English might or might not use it, but here the difference is straightforward: o points to a specific shoot.

Murchou is the pretérito perfeito simples in Portuguese, which usually corresponds to the simple past in English.

It comes from the verb murchar = to wilt.

Conjugation:

• eu murchei = I wilted
• tu murchaste = you wilted
• ele/ela/você murchou = he/she/it wilted

So murchou means wilted or has wilted, depending on context, but in a sentence like this English normally uses wilted.

Because murchou presents the wilting as a completed event.

• murchou = it wilted / it ended up wilting
• murchava = it was wilting / it used to wilt / it would wilt

So:

• O rebento murchou com o calor.
  = a finished result in the past
• O rebento murchava com o calor.
  = a repeated action, a description in progress, or a habitual effect of the heat

A learner can think of murchou as reporting what happened, while murchava often describes what was going on or what usually happened.

Literally, com o calor means with the heat.
In natural English, it usually means something like:

• because of the heat
• from the heat
• in the heat

In Portuguese, com can sometimes express the circumstance or cause accompanying something.

So in this sentence, com o calor explains what caused the shoot to wilt.

Because com is a natural, compact way to express that something happened under the effect of a condition.

These are all possible, but slightly different in tone:

• com o calor = with the heat / in the heat / from the heat
• por causa do calor = because of the heat
• devido ao calor = due to the heat

Com o calor sounds simple and idiomatic.
Por causa do calor is more explicitly causal.
Devido ao calor is a bit more formal.

Yes, you can absolutely say:

• Com o calor, o rebento murchou.

That is perfectly natural. It puts a little more emphasis on the condition or cause first.

Both are correct:

• O rebento murchou com o calor.
• Com o calor, o rebento murchou.

The original version is the more neutral subject + verb + complement order.

Because Portuguese verbs agree with the person and number of the subject, not with its gender.

So whether the subject is masculine or feminine, singular ele/ela uses the same verb form:

• O rebento murchou.
• A planta murchou.

Both use murchou because both are third person singular.

Gender affects articles and adjectives much more often than verb endings.

In European Portuguese, murchou is approximately pronounced like:

moor-SHOH
with the stress on the last syllable

A rougher European Portuguese pronunciation is often written as:

• mur-SHOH

A few points:

• ch in Portuguese sounds like sh
• the final -ou in European Portuguese is usually a clear diphthong, roughly like ohw
• the r in mur- is the single Portuguese r, not the strong guttural sound of initial r

If you want an IPA-style guide, a common approximation is /muɾˈʃow/.

No. Its most basic meaning is for plants or flowers becoming limp or wilted, but it can also be used more figuratively.

For example, it can suggest:

• losing freshness
• drooping
• fading emotionally or physically

So while this sentence is clearly about a plant, you may also hear figurative uses in literature or expressive speech.

Yes. Depending on the exact botanical meaning, Portuguese may also use words like:

• broto
• gomo
• rebroto in some contexts

But rebento is a good word for a young shoot/sprout.

For a learner of European Portuguese, it is worth remembering that plant vocabulary can be a bit context-dependent, so the best English equivalent may vary between shoot, sprout, bud, or new growth.

In theory, yes, because both rebento and murchar can have figurative uses in some contexts. But on its own, this sentence strongly suggests the literal meaning:

• a plant shoot
• wilted because of heat

Without a special context, a Portuguese speaker would most naturally read it literally.